The store has a coupon for $10 off and a discount of 20%
C for the price after the coupon is applied.
So from the statement 2, you can realize there are two types of discounts:
The discount offered by the coupon
The discount offered by 20%
Since we need to write a function just for the coupon, then we don't include the discount offered as percentage, then we subtract the coupon from the original price: