Imagine a question and stream-of-consciousness explanation for which this is the answer: 27
Question: 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?
Stream-of-consciousness: The books will cost $40 because 8 x 5 = 40. He needs to save up $27 because 40 - 13 = 27.