conversations.from: human
conversations.value: I'm stuck on this math problem: Anna is trying to buy books for her local library. She had a budget of $16, and she has already spent $4. She also bought 2 books today, and both books cost her the same amount of money. If Anna has $2 left in her budget, how much did each of the books cost?
  Can you help?
conversations.from: assistant
conversations.value: Anna had already spent some money, so she started the day with $16 – $4 = $12.
  She has money left in the budget, so she spent a total of $12 – $2 = $10 on the books.
  Therefore each book cost her $10 / 2 = $5.