conversations.from: human
conversations.value: David found $12 on the street. He then gave it to his friend Evan who has $1 and needed to buy a watch worth $20. How much does Evan still need?
  Give me a clear explanation.
conversations.from: assistant
conversations.value: The total amount Evan has is $1 + $12 = $13.
  So Evan still needs $20 - $13 = $7.