from typing import List


def sum_list(lst: List[int]) -> int:
    """Takes a list of numbers, and returns the sum of the numbers in that list.
    Cannot use the built in function `sum`.

     Args:
         lst - a list of numbers

     Returns:
         the sum of the passed in list
     """
    result = 0
    slcounter = len(lst) - 1

    while slcounter >= 0:
        result = result + lst[slcounter]
        slcounter = slcounter - 1

    return result