A company's profit is equal to the revenue it generates minus the cost of producing and selling the product. The revenue function for a certain product is R(n)=80n and its cost function is 20n+200, where n is the number of units made and sold. What is the product function?

If the total revenue for n units is given by R(n), and the total cost is C(n), then the profit function P(n) for any arbitrary n units is simply

P(n) = R(n) - C(n).

That's the generic layout. You replace R(n) and C(n) by the specific algebraic expressions you have for each, and simplify.