Answer:
If P= price of the hardcover book, then
We have to spend $25-P, if P<$25; or $0 if P>= $25
Step-by-step explanation:
Lets call P the price of the hardcover book, in $. We can suppose that P is less than 25, otherwise we shoudnt spend on anything else to get the free shipping. If X is the amount that we have to spend to reach 25, then we get that P+X = 25. If P is known, we can obtain X by substracting P in both sides, therefore
X = 25-P
We conclude that if the price of the book P is less than 25, then we have to spend $25-P. Otherwise we have to spend 0.
