human
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?
assistant
How much will the books cost? ** The books will cost $40 because 8 x 5 = <<8*5=40>>40
How much does Tommy need to save up? ** He needs to save up $27 because 40 - 13 = <<40-13=27>>27
#### 27