Chapter 1.4, Problem 12SBE

Getting a Formula In Exercises S-4 through S-13, a verbal description of a function is given. Use a formula to express the function.

With no advertising, your newspaper has a circulation of $8000$ papers. For each dollar you spend on advertising, your newspaper circulation increased by $5$ papers. You earn a profit (taking into account advertising expense) of $7$ cents for each paper sold, but you must pay $\$400$ to have the papers delivered. Find a formula that gives the total profit $P$, in dollars, that you earn if you spend $a$ dollars on advertising.