Josh paid for three books with two $20 bills. He received $1 in change. Each book was the same price. How much did each book cost?

I found this answer on another question so hope this helps.

The total payment is:
P = 2 * ($ 20) = $ 40
The change is:
C = 1 $
The total cost is then:
CT = P-C = 40 $ -1 $ = 39 $
"each book was the same price":
Book price = ($ 39/3) = $ 13

each book cost:
Book price = $13