function solve() {
   const n = Number(read());
   const a = readArray(Number);
   const b = readArray(Number);
   const diff = [];
   let sumDiff = 0;
   for (let i = 0; i < n; i++) {
      diff[i] = a[i] - b[i];
      sumDiff += diff[i];
   }
   if (sumDiff !== 0) {
      write(-1);
      return;
   }
   const ans = [];
   while(true) {
      const i = diff.findIndex((x) => x > 0);
      const j = diff.findIndex((x) => x < 0);
      if (i === -1) {
         break;
      }
      diff[i]--;
      diff[j]++;
      ans.push((i + 1) + ' ' + (j + 1));
   }
   write(ans.length);
   ans.forEach(write);
}

function init() {
   try {
      var T;
      T = 1;
      T = Number(read());
      for (var t = 0; t < T; t++) {
         solve();
      }
   } catch (e) {
      write(e + e.stack);
   }
}

function modPow(a, n, mod) {
   let d = a;
   let curN = n;
   let ans = 1n;
   while(curN) {
      if (curN & 1n) {
         ans = modMul(ans, d, mod);
      }
      curN >>= 1n;
      d = modMul(d, d, mod);
   }
   return ans;
}

function modMul(a, b, mod) {
   return (a * b) % mod;
}

function modSum(a, b, mod) {
   return (a + b) % mod;
}

function modDiff(a, b, mod) {
   return (a + mod - b) % mod;
}

function isZero(num) {
   if (typeof num === 'bigint') {
      return num === 0n;
   }
   return num === 0;
}
function div(a, b) {
   if (typeof a !== typeof b) {
      throw new Error('Different types on division');
   }
   if (typeof a === 'bigint') {
      return a / b;
   }
   return Math.floor(a / b);
}

function gcd(x, y) {
   if (isZero(y)) {
      return x;
   }
   return gcd(y, x % y);
}

function lcm(x, y) {
   return div(x * y, gcd(x, y));
}

function allIndexOf(arr, value) {
   var index = arr.indexOf(value)
   var ans = [];
   while (index !== -1) {
      ans.push(index);
      index = arr.indexOf(value, index + 1);
   }
   return ans;
}

function xor(a, b, k) {
   if (k === 2) {
      return a ^ b;
   }
}

function decToBin(num) {
   let n = num;
   const ans = [];
   while(n > 0) {
      ans.push(n & 1);
      n = (n >> 1);
   }
   return ans;
}

function binToDec(binN) {
   let ans = 0;
   for (let i = binN.length - 1; i >= 0; i--) {
      ans = ((ans << 1) | binN[i]);
   }
   return ans;
}

function sortF(a, b) {
   if (a < b) {
      return -1;
   }
   if (a > b) {
      return 1;
   }
   return 0;
}

function readArray(f) {
   return read().split(' ').map(f);
}

var isNode = typeof console !== 'undefined';
var MEMORY = [];
var MEMORY_INDEX = 0;
if (isNode) {
   var fs = require('fs');
   var path = require('path');

   var inTextName;
   var outTextName;

   var needWriteFile = false;

   var writeResult = '';
   if (process.argv.length === 5) {
      inTextName = process.argv[3];
      outTextName = process.argv[4];
   }

   if (inTextName) {
      fs.readFile(path.join(__dirname, inTextName), 'utf8', (err, data) => {
         MEMORY = data.split('\r\n');
         init();
         if (needWriteFile) {
            fs.writeFile(path.join(__dirname, outTextName), writeResult, (err) => {
               err ? console.error(err) : console.log('good')
            });
         }
      });
   } else {
      MEMORY = fs.readFileSync(0, 'utf-8').split('\r\n');
      init();
   }
} else {
   init();
}

function write(value) {
   if (needWriteFile) {
      writeResult += value + '\n';
      return;
   }
   isNode ? console.log('' + value) : print('' + value);
}
function read() {
   return isNode ? MEMORY[MEMORY_INDEX++] : readline();
}
function readAll() {
   return isNode && MEMORY;
}

var input = +readline();
for(var i = 0; i < input; i ++) {
    var num = +readline();
    var a = readline().split(' ').map(Number);
    var b = readline().split(' ').map(Number);
    var sum = 0;
    for(var j = 0; j < num; j ++) sum += a[j] - b[j];
    if(sum !== 0) print('-1');
    else {
        var result = [];
        for(var k = 0; k < num; k ++) {
            while(a[k] < b[k]) {
                a[k] ++;
                for(var m = 0; m < num; m ++) {
                    if(a[m] > b[m]) {
                        a[m] --;
                        result.push([m + 1, k + 1]);
                        sum ++;
                        break;
                    }
                }
            }
        }
        print(sum);
        result.forEach((x) => print(x.join(' ')));
    }
}

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 07/11/21 afternoon
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let d1 = [];
    let d2 = [];
    for (let i = 0; i < n; i++) {
        for (let j = 0; j < a[i] - b[i]; j++) d1.push(i);
        for (let j = 0; j < b[i] - a[i]; j++) d2.push(i);
    }
    // if (d1.length != d2.length) return pr(-1);
    pr(d1.length);
    for (let i = 0; i < d1.length; i++) pr((d1[i] + 1) + " " + (d2[i] + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// 07/11/21 afternoon
const solve = (n, a, b) => {
    let d1 = [];
    let d2 = [];
    for (let i = 0; i < n; i++) {
        for (let j = 0; j < a[i] - b[i]; j++) d1.push(i);
        for (let j = 0; j < b[i] - a[i]; j++) d2.push(i);
    }
    if (d1.length != d2.length) return pr(-1);
    pr(d1.length);
    for (let i = 0; i < d1.length; i++) pr((d1[i] + 1) + " " + (d2[i] + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

let stop = '';
process.stdin.on('data', c => stop += c);
process.stdin.on('end', () => {
    const {EOL} = require('os');
    const lines = stop.split(EOL);
    var t = lines[0];
    var n = 0;
    var a = 0;
    for(i = 1; i <= t * 3; i++){
        if(i % 3 == 1){
            n = lines[i];
        }else if(i % 3 == 2){
            a = lines[i].split(' ').map(Number);
        }else{
            var b = lines[i].split(' ').map(Number);
            var sn = 0;
            var sp = 0;
            var v = [];
            var v1 = [];
            for(j = 0; j < n; j++){
                var x = a[j] - b[j];
                if(x > 0){
                    sn += x;
                    while(x--){
                        v.push(j);
                    }
                }else if(x < 0){
                    x *= -1;
                    sp += x;
                    while(x--){
                        v1.push(j);
                    }
                }
            }
            if(sn == sp){
                console.log(sn);
                for(j = 0; j < sn; j++){
                    console.log(v[j] + 1, v1[j] + 1);
                }
            }else{
                console.log(-1);
            }
        }
    }
});

let stop = '';
process.stdin.on('data', c => stop += c);
process.stdin.on('end', () => {
    const {EOL} = require('os');
    const lines = stop.split(EOL);
	var t = lines[0];
	var n = 0;
	var a = 0;
	for(i = 1; i <= t * 3; i++){
	    var b = lines[i].split(' ').map(Number);
        if(i % 3 == 1){
            n = lines[i];
        }else if(i % 3 == 2){
            a = lines[i].split(' ').map(Number);
        }else{
            var v = [];
            var v1 = [];
            var sp = 0;
        	var sn = 0;
            for(j = 0; j < n; j++){
                var x = a[j] - b[j];
                if(x > 0){
                    sp += x;
                    while(x--){
                        v.push(j);
                    }
                }else if(x < 0){
                    x *= -1;
                    sn += x;
                    while(x--){
                        v1.push(j);
                    }
                }else if(x === 0){
                    continue;
                }
            }
            if(sp == sn){
                console.log(sp);
                for(j = 0; j < sn; j++){
                    console.log(v[j] + 1, v1[j] + 1);
                }
            }else{
                console.log(-1);
            }
        }
    }
});

//Don't have to see. start------------------------------------------
var read = require('readline').createInterface({
	input: process.stdin, output: process.stdout
});
var obj; var inLine = []; var outputList = [];var retcode = new Set();
read.on('line', function(input){
	var tmp = input.split(' ');
	for(var i = 0; i < tmp.length; i++){
		inLine.push(tmp[i]);
		if(i == tmp.length - 1){
			retcode.add(inLine.length);
		}
	}
});
read.on('close', function(){
	obj = init(inLine);
	console.error('\n↑入力 ↓出力');
	Main();
	console.log(myconv(outputList, 9));
});
function makeClone(obj){return (obj instanceof Set) ? new Set(Array.from(obj)) : JSON.parse(JSON.stringify(obj));}
function nextArray(size, code){
	var ret = new Array(size);
	for(var i = 0; i < size; i++){
		if(code == 'int'){
			ret[i] = nextInt();
		}else if(code == 'long'){
			ret[i] = BigInt(next());
		}else{
			ret[i] = next();
		}
	}
	return ret;
}
function nextIntArray(size){return nextArray(size, 'int');} function nextStrArray(size){return nextArray(size, 'str');} function nextLongArray(size){return nextArray(size, 'long');}
function nextCharArray(){return myconv(next(),6);}
function next(){return obj.next();} function hasNext(){return obj.hasNext();} function nextInt(){return myconv(next(),1);} function nextLong(){return BigInt(next());}
function getCountMap(list){
	var map = {};
	for(var i = 0; i < list.length; i++){
		if(map[list[i]] == null){
			map[list[i]] = 0;
		}
		map[list[i]]++;
	}
	return map;
}
function init(input){
	return {
		list : input, index : 0, max : input.length,
		hasNext : function(){return (this.index < this.max);},
		next : function(){if(this.hasNext()){return this.list[this.index++];}else{throw 'ArrayIndexOutOfBoundsException ‚There is no more input';}},
		isReturn : function(){return retcode.has(this.index);}
	};
}
function myout(s){outputList.push(s);}
function myerr(s){console.error('debug:' + require('util').inspect(s,false,null));}
function isReturn(){return obj.isReturn();}
//param "no" is
//unknown or outlier : return i. 1: parseInt.
//2: split space. 4: split space and parseInt.
//6: split 1 character. 7: split 1 character and parseInt.
//8: join space. 9: join nextline. 0: join no character.
function myconv(i,no){try{switch(no){case 1:return parseInt(i);case 2:return i.split(' ');case 4:return i.split(' ').map(Number);case 6:return i.split('');case 7:return i.split('').map(Number);case 8:return i.join(' ');case 9:return i.join('\n');case 0:return i.join('');default:return i;}}catch(e){return i;}}

//Don't have to see. end------------------------------------------
function Main(){
	var t = nextInt();
	while(hasNext()){
		var N = nextInt();
		var A = nextIntArray(N);
		var B = nextIntArray(N);
		var lsum = 0;
		var rsum = 0;
		for(var i = 0; i < N; i++){
			lsum += A[i];
			rsum += B[i];
		}
		if(lsum != rsum){
			myout(-1);
			continue;
		}
		var output = [];
		var sumlist = new Array(N);
		for(var i = 0; i < N; i++){
			sumlist[i] = A[i] - B[i];
		}
		for(var i = 0; i < N; i++){
			if(sumlist[i] != 0){
				for(var j = 0; j < N; j++){
					if(sumlist[i] < 0 && sumlist[j] > 0){
						while(sumlist[i] != 0 && sumlist[j] != 0){
							output.push((j + 1) + " " + (i + 1));
							sumlist[i]++;
							sumlist[j]--;
						}
					}else if(sumlist[i] > 0 && sumlist[j] < 0){
						while(sumlist[i] != 0 && sumlist[j] != 0){
							output.push((i + 1) + " " + (j + 1));
							sumlist[i]--;
							sumlist[j]++;
						}
					}
				}
			}
		}
		myout(output.length);
		if(output.length > 0){
			myout(myconv(output, 9));
		}
	}
}

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', inputStdin => {
    inputString += inputStdin;
});

process.stdin.on('end', _ => {
    inputString = inputString.trim().split('\n').map(str => str.trim());

    main();
});

function readLine() {
    return inputString[currentLine++];
}
function main()
{
    //const name=readLine();
    //console.log(name);

    let test=readLine();
    while(test--)
    {
        n=readLine();
        let a=[n],b=[n];
        aa=readLine();
        aa=aa.split(" ");
        for(i=0;i<n;i++)
            a[i]=parseInt(aa[i]);
        bb=readLine();
        bb=bb.split(" ");
        let sum_p=0,sum_n=0;
        decrease=[],increase=[];
        for(i=0;i<n;i++)
        {
            b[i]=parseInt(bb[i]);
            if((b[i]-a[i])>0)
            {
                sum_p+=b[i]-a[i];
                increase.push([i,b[i]-a[i]])
                //increase.push_back(mp(i,b[i]-a[i]));
            }
            else if((b[i]-a[i])<0)
            {
                sum_n+=a[i]-b[i];
                decrease.push([i,a[i]-b[i]]);
                //decrease.push_back(mp(i,a[i]-b[i]));
            }
        }
        if(sum_p!=sum_n)
        {
            console.log(-1);
            //cout<<"-1"<<endl;
            continue;
        }
        if(sum_p==0)
        {
            console.log(0);
            //cout<<0<<endl;
            continue;
        }
        console.log(sum_p);
        //cout<<sum_p<<endl;
        for(pos1=0,pos2=0,i=0;i<sum_p;i++)
        {
            if(decrease[pos1][1]==0)
                pos1++;
            //decrease[pos1][0]+1;
            decrease[pos1][1]--;
            if(increase[pos2][1]==0)
                pos2++;
            console.log(decrease[pos1][0]+1,increase[pos2][0]+1)//<<endl;
            increase[pos2][1]--;
        }
    }
}

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    let se = new Set();
    while (true) {
        let flag = true;
        for (let i = 0; i < n; i++) {
            if (a[i] != b[i]) {
                if (se.has(i)) continue;
                flag = false;
                let j;
                for (let idx = n - 1; ~idx; idx--) {
                    if (se.has(idx)) continue;
                    if (a[idx] == b[i]) {
                        j = idx;
                        break;
                    }
                }
                // se.add(j);
                se.add(i);
                // let j = a.lastIndexOf(b[i]);
                if (a[i] > a[j]) {
                    let step = a[i] - a[j];
                    res += step;
                    while (step--) {
                        a[i]--;
                        a[j]++;
                        d.push([i, j]);
                    }
                } else if (a[i] < a[j]) {
                    let step = a[j] - a[i];
                    res += step;
                    while (step--) {
                        a[i]++;
                        a[j]--;
                        d.push([j, i]);
                    }
                }
            }
        }
        // pr(a, flag);
        if (flag) break;
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    let se = new Set();
    while (true) {
        let flag = true;
        for (let i = 0; i < n; i++) {
            if (se.has(i)) continue;
            if (a[i] != b[i]) {
                flag = false;
                let j;
                for (let idx = n - 1; ~idx; idx--) {
                    if (se.has(idx)) continue;
                    if (a[idx] == b[i]) {
                        j = idx;
                        break;
                    }
                }
                se.add(j);
                se.add(i);
                // let j = a.lastIndexOf(b[i]);
                if (a[i] > a[j]) {
                    let step = a[i] - a[j];
                    res += step;
                    while (step--) {
                        a[i]--;
                        a[j]++;
                        d.push([i, j]);
                    }
                } else if (a[i] < a[j]) {
                    let step = a[j] - a[i];
                    res += step;
                    while (step--) {
                        a[i]++;
                        a[j]--;
                        d.push([j, i]);
                    }
                }
            }
        }
        // pr(a, flag);
        if (flag) break;
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    let se = new Set();
    while (true) {
        let flag = true;
        for (let i = 0; i < n; i++) {
            if (se.has(i)) continue;
            if (a[i] != b[i]) {
                flag = false;
                let j;
                for (let idx = n - 1; ~idx; idx--) {
                    // if (se.has(idx)) continue;
                    if (a[idx] == b[i]) {
                        j = idx;
                        break;
                    }
                }
                se.add(j);
                se.add(i);
                // let j = a.lastIndexOf(b[i]);
                if (a[i] > a[j]) {
                    let step = a[i] - a[j];
                    res += step;
                    while (step--) {
                        a[i]--;
                        a[j]++;
                        d.push([i, j]);
                    }
                } else if (a[i] < a[j]) {
                    let step = a[j] - a[i];
                    res += step;
                    while (step--) {
                        a[i]++;
                        a[j]--;
                        d.push([j, i]);
                    }
                }
            }
        }
        // pr(a, flag);
        if (flag) break;
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    let se = new Set();
    for (let i = 0; i < n; i++) {
        if (a[i] != b[i]) {
            let j;
            for (let idx = n - 1; ~idx; idx--) {
                if (se.has(idx)) continue;
                if (b[idx] == a[i]) {
                    j = idx;
                    break;
                }
            }
            se.add(j);
            // let j = b.lastIndexOf(a[i]);
            if (a[i] > a[j]) {
                let step = a[i] - a[j];
                res += step;
                while (step--) {
                    a[i]--;
                    a[j]++;
                    d.push([i, j]);
                }
            } else if (a[i] < a[j]) {
                let step = a[j] - a[i];
                res += step;
                while (step--) {
                    a[i]++;
                    a[j]--;
                    d.push([j, i]);
                }
            }
        }
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    for (let i = 0; i < n; i++) {
        if (a[i] != b[i]) {
            let j = b.lastIndexOf(a[i]);
            if (a[i] > a[j]) {
                let step = a[i] - a[j];
                res += step;
                while (step--) {
                    a[i]--;
                    a[j]++;
                    d.push([i, j]);
                }
            } else if (a[i] < a[j]) {
                let step = a[j] - a[i];
                res += step;
                while (step--) {
                    a[i]++;
                    a[j]--;
                    d.push([j, i]);
                }
            }
        }
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    for (let i = 0; i < n; i++) {
        if (a[i] != b[i]) {
            let j = b.indexOf(a[i]);
            if (a[i] > a[j]) {
                let step = a[i] - a[j];
                res += step;
                while (step--) {
                    a[i]--;
                    a[j]++;
                    d.push([i, j]);
                }
            } else if (a[i] < a[j]) {
                let step = a[j] - a[i];
                res += step;
                while (step--) {
                    a[i]++;
                    a[j]--;
                    d.push([j, i]);
                }
            }
        }
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    while (true) {
        let flag = true;
        for (let i = 0; i < n; i++) {
            if (a[i] != b[i]) {
                flag = false;
                let j = b.indexOf(a[i]);
                if (a[i] > a[j]) {
                    let step = a[i] - a[j];
                    res += step;
                    while (step--) {
                        a[i]--;
                        a[j]++;
                        d.push([i, j]);
                    }
                } else if (a[i] < a[j]) {
                    let step = a[j] - a[i];
                    res += step;
                    while (step--) {
                        a[i]++;
                        a[j]--;
                        d.push([i, j]);
                    }
                }
            }
        }
        if (flag) break;
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    for (let i = 0; i < n; i++) {
        let j = b.indexOf(a[i]);
        if (a[i] > a[j]) {
            let step = a[i] - a[j];
            res += step;
            while (step--) {
                a[i]--;
                a[j]++;
                d.push([i, j]);
            }
        } else if (a[i] < a[j]) {
            let step = a[j] - a[i];
            res += step;
            while (step--) {
                a[i]++;
                a[j]--;
                d.push([i, j]);
            }
        }
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr((i + 1) + " " + (j + 1));
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

///////////////////////////////// pre-define ////////////////////////////////////////////////////////////////////////////////
const pr = console.log;
const assert = (condition) => { if (!condition) throw new Error("Assertion failed"); }
const mi = Math.min;
const mx = Math.max;
const mxll = (...args) => args.reduce((m, e) => e > m ? e : m);
const mill = (...args) => args.reduce((m, e) => e < m ? e : m);
const sqll = (v) => { if (v < 0n) throw 'negative input'; if (v < 2n) return v; const dfs = (n, x0) => { let x1 = ((n / x0) + x0) >> 1n; if (x0 === x1 || x0 === (x1 - 1n)) return x0; return dfs(n, x1); }; return dfs(v, 1n); }; // has >> 0
const abs = Math.abs;
const fl = Math.floor;
const int = parseInt;
const ce = Math.ceil;
const sq = Math.sqrt;
const lge = Math.log;
const lg2 = Math.log2;
const lg10 = Math.log10;
const ll = BigInt;
const combination = (m, n) => { return factorial(m, n) / factorial(n, n); };
const factorial = (m, n) => { let num = 1n; let cnt = 0; for (let i = ll(m); i > 0; i--) { if (cnt == n) break; num *= i; cnt++; } return num; };
const gcd = (a, b) => b == 0 ? a : gcd(b, a % b);
const lcm = (a, b) => (a / gcd(a, b)) * b;
const bitCount = (n) => { n = n - ((n >> 1) & 0x55555555); n = (n & 0x33333333) + ((n >> 2) & 0x33333333); return ((n + (n >> 4) & 0xF0F0F0F) * 0x1010101) >> 24; };
const powmod = (a, b, mod) => { let r = 1n; while (b > 0n) { if (b % 2n == 1) r = r * a % mod; b >>= 1n; a = a * a % mod; } return r; };
const amax = (a) => mx.apply(Math, a);
const amin = (a) => mi.apply(Math, a);
const sm = (a) => a.reduce(((x, y) => x + y), 0);
const aeq = (a, b) => a.length === b.length && a.every((v, i) => v === b[i]);
const swap = (a, i, j) => [a[i], a[j]] = [a[j], a[i]];
const stin = (a) => a.sort((x, y) => x - y);
const stde = (a) => a.sort((x, y) => y - x);
const sortPart = (a, k) => { let l = a.slice(0, k); l.sort((x, y) => x - y); let r = a.slice(k); return l.concat(r); }; // sort first kth
const initialize2DArrayNew = (n, m) => { let data = []; for (let i = 0; i < n; i++) { let tmp = Array(m).fill(0); data.push(tmp); } return data; };
const initialize3DArray = (n, m, p) => { let res = []; for (let i = 0; i < n; i++) { let data = []; for (let j = 0; j < m; j++) { let tmp = new Array(p).fill(0); data.push(tmp); } res.push(data); } return res; };
const stmkey_in = (m) => new Map([...m].sort((x, y) => x[0] - y[0]));
const stmkey_de = (m) => new Map([...m].sort((x, y) => y[0] - x[0]));
const stmvalue_in = (m) => new Map([...m].sort((x, y) => x[1] - y[1]));
const stmvalue_de = (m) => new Map([...m].sort((x, y) => y[1] - x[1]));
const counter = (a_or_s) => { let map = new Map(); for (const i of a_or_s) map.set(i, map.get(i) + 1 || 1); return map; };
const counter_value_in_indexA_in = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).push(i); } return m; };
const counter_value_in_indexA_de = (a_or_s) => { let m = new Map(); let n = a_or_s.length; for (let i = 0; i < n; i++) { if (!m.has(a_or_s[i])) m.set(a_or_s[i], []); m.get(a_or_s[i]).unshift(i); } return m; };
const reverse2 = (s) => { let res = ""; for (let i = s.length - 1; i >= 0; i--) { res += s[i]; } return res; };
const isPalindrome = (s) => { let n = s.length; let i = 0; let j = n - 1; while (i < j) { if (s[i++] != s[j--]) return false; } return true; };
const ups = (s, i, c) => s.slice(0, i) + c + s.slice(i + 1);
const isSubsequence = (s, t) => { let sn = s.length; let tn = t.length; let i = j = 0; while (i < sn && j < tn) { if (s[i] == t[j]) { i++; j++; } else { i++; } } return j == tn; };
//////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
/**
 * 07/11/21 morning
 * https://codeforces.com/contest/1546/problem/A
 */
const solve = (n, a, b) => {
    let sa = sm(a);
    let sb = sm(b);
    if (sa != sb) return pr(-1);
    let res = 0;
    let d = [];
    for (let i = 0; i < n; i++) {
        let j = b.indexOf(a[i]);
        if (a[i] > a[j]) {
            let step = a[i] - a[j];
            res += step;
            while (step--) {
                a[i]--;
                a[j]++;
                d.push([i, j]);
            }
        } else if (a[i] < a[j]) {
            let step = a[j] - a[i];
            res += step;
            while (step--) {
                a[i]++;
                a[j]--;
                d.push([i, j]);
            }
        }
    }
    // pr(a, b)
    pr(res);
    for (const [i, j] of d) pr(i + " " + j);
};

const main = () => {
    const readline = require('readline');
    const rl = readline.createInterface({
        input: process.stdin,
        output: process.stdout
    });
    let input = [];
    rl.on('line', (line) => {
        input.push(line.split(" ").map(x => Number(x)));
    });
    rl.on('close', () => {
        let t = input[0][0];
        let i = 1;
        while (t--) {
            solve(input[i][0], input[i + 1], input[i + 2]);
            i += 3;
        }
    });
};

main()

let stop = '';
process.stdin.on('data', c => stop += c);
process.stdin.on('end', () => {
    const {EOL} = require('os');
    const lines = stop.split(EOL);
    var t = lines[0];
    var n = 0;
    var a = 0;
    for(i = 1; i <= t * 3; i++){
        if(i % 3 == 1){
            n = lines[i];
        }else if(i % 3 == 2){
            a = lines[i].split(' ').map(Number);
        }else{
            var b = lines[i].split(' ').map(Number);
            var sn = 0;
            var sp = 0;
            var v = [];
            var v1 = [];
            for(j = 0; j < n; j++){
                var x = a[j] - b[j];
                if(x > 0){
                    sn += x;
                    while(x--){
                        v.push(x);
                    }
                }else if(x < 0){
                    x *= -1;
                    sp += x;
                    while(x--){
                        v1.push(x);
                    }
                }
            }
            if(sn == sp){
                console.log(sn);
                for(j = 0; j < sn; j++){
                    console.log(v[j] + 1, v1[j] + 1);
                }
            }else{
                console.log(-1);
            }
        }
    }
});

//Don't have to see. start------------------------------------------
var read = require('readline').createInterface({
	input: process.stdin, output: process.stdout
});
var obj; var inLine = []; var outputList = [];var retcode = new Set();
read.on('line', function(input){
	var tmp = input.split(' ');
	for(var i = 0; i < tmp.length; i++){
		inLine.push(tmp[i]);
		if(i == tmp.length - 1){
			retcode.add(inLine.length);
		}
	}
});
read.on('close', function(){
	obj = init(inLine);
	console.error('\n↑入力 ↓出力');
	Main();
	console.log(myconv(outputList, 9));
});
function makeClone(obj){return (obj instanceof Set) ? new Set(Array.from(obj)) : JSON.parse(JSON.stringify(obj));}
function nextArray(size, code){
	var ret = new Array(size);
	for(var i = 0; i < size; i++){
		if(code == 'int'){
			ret[i] = nextInt();
		}else if(code == 'long'){
			ret[i] = BigInt(next());
		}else{
			ret[i] = next();
		}
	}
	return ret;
}
function nextIntArray(size){return nextArray(size, 'int');} function nextStrArray(size){return nextArray(size, 'str');} function nextLongArray(size){return nextArray(size, 'long');}
function nextCharArray(){return myconv(next(),6);}
function next(){return obj.next();} function hasNext(){return obj.hasNext();} function nextInt(){return myconv(next(),1);} function nextLong(){return BigInt(next());}
function getCountMap(list){
	var map = {};
	for(var i = 0; i < list.length; i++){
		if(map[list[i]] == null){
			map[list[i]] = 0;
		}
		map[list[i]]++;
	}
	return map;
}
function init(input){
	return {
		list : input, index : 0, max : input.length,
		hasNext : function(){return (this.index < this.max);},
		next : function(){if(this.hasNext()){return this.list[this.index++];}else{throw 'ArrayIndexOutOfBoundsException ‚There is no more input';}},
		isReturn : function(){return retcode.has(this.index);}
	};
}
function myout(s){outputList.push(s);}
function myerr(s){console.error('debug:' + require('util').inspect(s,false,null));}
function isReturn(){return obj.isReturn();}
//param "no" is
//unknown or outlier : return i. 1: parseInt.
//2: split space. 4: split space and parseInt.
//6: split 1 character. 7: split 1 character and parseInt.
//8: join space. 9: join nextline. 0: join no character.
function myconv(i,no){try{switch(no){case 1:return parseInt(i);case 2:return i.split(' ');case 4:return i.split(' ').map(Number);case 6:return i.split('');case 7:return i.split('').map(Number);case 8:return i.join(' ');case 9:return i.join('\n');case 0:return i.join('');default:return i;}}catch(e){return i;}}

//Don't have to see. end------------------------------------------
function Main(){
	var t = nextInt();
	while(hasNext()){
		var N = nextInt();
		var A = nextIntArray(N);
		var B = nextIntArray(N);
		var lsum = 0;
		var rsum = 0;
		for(var i = 0; i < N; i++){
			lsum += A[i];
			rsum += B[i];
		}
		if(lsum != rsum){
			myout(-1);
			continue;
		}
		var output = [];
		var sumlist = new Array(N);
		for(var i = 0; i < N; i++){
			sumlist[i] = A[i] - B[i];
		}
		for(var i = 0; i < N; i++){
			if(sumlist[i] != 0){
				for(var j = 0; j < N; j++){
					if(sumlist[i] < 0 && sumlist[j] > 0){

						output.push((j + 1) + " " + (i + 1));
						sumlist[i]++;
						sumlist[j]--;
					}else if(sumlist[i] > 0 && sumlist[j] < 0){
						output.push((i + 1) + " " + (j + 1));
						sumlist[i]--;
						sumlist[j]++;
					}
				}
			}
		}
		for(var i = 0; i < N; i++){
			if(sumlist[i] != 0){
				for(var j = 0; j < N; j++){
					if(sumlist[i] < 0 && sumlist[j] > 0){

						output.push((j + 1) + " " + (i + 1));
						sumlist[i]++;
						sumlist[j]--;
					}else if(sumlist[i] > 0 && sumlist[j] < 0){
						output.push((i + 1) + " " + (j + 1));
						sumlist[i]--;
						sumlist[j]++;
					}
				}
			}
		}
		myerr(sumlist);
		myout(output.length);
		if(output.length > 0){
			myout(myconv(output, 9));
		}
	}
}

process.stdin.resume();
process.stdin.setEncoding('utf-8');

let inputString = '';
let currentLine = 0;

process.stdin.on('data', inputStdin => {
    inputString += inputStdin;
});

process.stdin.on('end', _ => {
    inputString = inputString.trim().split('\n').map(str => str.trim());

    main();
});

function readLine() {
    return inputString[currentLine++];
}
function main()
{
    //const name=readLine();
    //console.log(name);

    let test=readLine();
    while(test--)
    {
        n=readLine();
        let a=[n],b=[n];
        aa=readLine();
        aa=aa.split(" ");
        for(i=0;i<n;i++)
            a[i]=parseInt(aa[i]);
        bb=readLine();
        bb=bb.split(" ");
        let sum_p=0,sum_n=0;
        decrease=[],increase=[];
        for(i=0;i<n;i++)
        {
            b[i]=parseInt(bb[i]);
            if((b[i]-a[i])>0)
            {
                sum_p+=b[i]-a[i];
                increase.push([i,b[i]-a[i]])
                //increase.push_back(mp(i,b[i]-a[i]));
            }
            else if((b[i]-a[i])<0)
            {
                sum_n+=a[i]-b[i];
                decrease.push([i,a[i]-b[i]]);
                //decrease.push_back(mp(i,a[i]-b[i]));
            }
        }
        if(sum_p!=sum_n)
        {
            console.log(-1);
            //cout<<"-1"<<endl;
            continue;
        }
        if(sum_p==0)
        {
            console.log(0);
            //cout<<0<<endl;
            continue;
        }
        console.log(sum_p);
        //cout<<sum_p<<endl;
        for(pos1=0,pos2=0,i=0;i<sum_p;i++)
        {
            if(decrease[pos1][1]==0)
                pos1++;
            //decrease[pos1][0]+1;
            decrease[pos1][1]--;
            if(increase[pos2][1]==0)
                pos2++;
            console.log(decrease[pos1][0]+1,increase[pos2][0]+1)//<<endl;
            increase[pos2].second--;
        }
    }
}


'use strict';
const { throws } = require('assert');

 /*jslint node:true, browser:true, es6:true*/
const print = console.log
const E = {};
const lines = []
if (!process.env.JEST_WORKER_ID){
  const rl = require('readline').createInterface({ input: process.stdin, output: process.stdout })
  rl.on('line', line => {
      lines.push(line);
  });
  rl.on('close', main)
}
let rli = 0;
function readline() {
    return lines[rli++];
}
const l = process.env.DEBUG ? console.log : ()=>{};

module.exports = E;

const ra = ()=>readline().split(' ').map(a=>+a)

const MOD = 1e9+7;

const calc = (n, s)=>{
  n = BigInt(n);
  s = BigInt(s)
  return (s/(n*n)).toString(10)
};

function main() {
    let T = +readline()
    while (T--){
      let [n, s] = readline().split(' ');
      print(calc(n, s));
    }
}

E.calc = calc;

let buf='';

process.stdin.on('readable', function(){
    let chunk=process.stdin.read();
    if(chunk) buf+=chunk.toString();
})

process.stdin.on('end', function(){
    const {EOL}=require('os');
    let line=buf.split(EOL);
    let t=parseInt(line[0]);
    for(let _=1;_<=t;_++)
    {
        let [n,s]=line[_].split(' ');
        n=BigInt(n);
        s=BigInt(s);
        n=n*n;
        // console.log(s,n);
        let ans=''+s/n;
        console.log(ans);
    }
})

'use strict';
const { throws } = require('assert');

 /*jslint node:true, browser:true, es6:true*/
const print = console.log
const E = {};
const lines = []
if (!process.env.JEST_WORKER_ID){
  const rl = require('readline').createInterface({ input: process.stdin, output: process.stdout })
  rl.on('line', line => {
      lines.push(line);
  });
  rl.on('close', main)
}
let rli = 0;
function readline() {
    return lines[rli++];
}
const l = process.env.DEBUG ? console.log : ()=>{};

module.exports = E;

const ra = ()=>readline().split(' ').map(a=>+a)

const EPS = 1e-6;
const MOD = 1e9+7;

const calc = (n, s)=>{
  return Math.floor(s/(n*n)+EPS)
};

function main() {
    let T = +readline()
    while (T--){
      let [n, s] = ra();
      print(calc(n, s));
    }
}

E.calc = calc;

'use strict';
const { throws } = require('assert');

 /*jslint node:true, browser:true, es6:true*/
const print = console.log
const E = {};
const lines = []
if (!process.env.JEST_WORKER_ID){
  const rl = require('readline').createInterface({ input: process.stdin, output: process.stdout })
  rl.on('line', line => {
      lines.push(line);
  });
  rl.on('close', main)
}
let rli = 0;
function readline() {
    return lines[rli++];
}
const l = process.env.DEBUG ? console.log : ()=>{};

module.exports = E;

const ra = ()=>readline().split(' ').map(a=>+a)

const EPS = 1e-6;
const MOD = 1e9+7;

const calc = (n, s)=>{
  return Math.floor(s/(n*n))
};

function main() {
    let T = +readline()
    while (T--){
      let [n, s] = ra();
      print(calc(n, s));
    }
}

E.calc = calc;