Please Help!

Kyra has a manufacturer's coupon for $5 off a box of diapers and a store coupon for 20% off any purchase. The store will let you use both coupons, but it does not have a policy about which coupon you must use first. What order should she use the coupons to get the maximum discount on a $40 box of diapers?
A) It does not matter. Either way, she will spend the same amount.
B) There is not enough information since the tax rate is not given.
C) Kyra should use the $5 off coupon first and then the store coupon for 20% off.
D) Kyra should use the store coupon for 20% off first and then the $5 off coupon.