Final answer:
To find the percentage discount, calculate the difference between the regular price and the sale price, and divide it by the regular price. In this case, the percentage discount is 20%.
Step-by-step explanation:
To find the percentage discount, we need to calculate the difference between the regular price and the sale price, and then divide it by the regular price.
In this case, the regular price is $28 and Benson bought the book at $22.40.
The difference between the regular price and the sale price is $28 - $22.40 = $5.60.
To find the percentage discount, we divide the difference by the regular price and multiply by 100.
The percentage discount is (5.60 / 28) * 100 = 20%.