A small publisher plans to spend $1000 for advertising a paperback book and estimates the printing cost is $2.50 per book. The publisher will receive $7 for each book sold.

a. Find the function C = f(x) that gives the cost of producing x books.

b. Find the function R = g(x) that gives the revenue from selling x books.

c. Graph the cost and revenue functions; then find the number of books that must be sold for the publisher to break even.