conversations.from: human
conversations.value: Can you guide me through solving this problem: Tommy wants to earn enough money to buy 8 new books. Each book costs $5. If Tommy already has $13, how much does he need to save up?
conversations.from: assistant
conversations.value: The books will cost $40 because 8 x 5 = 40
  He needs to save up $27 because 40 - 13 = 27