conversations.from: human
conversations.value: Derek has $40. He spends $14 on lunch for himself, $11 for lunch for his dad, and $5 on more lunch for himself. His brother Dave has $50 and only spends $7 on lunch for his mom. How much more money does Dave have left than Derek?
  Give me a solution to this problem
conversations.from: assistant
conversations.value: Derek has 40-14-11-5 = 10 dollars left
  Dave has 50-7 = 43 dollars left.
  Dave has 43-10 = 33 more dollars left than Derek.