The marginal profit in dollars on Brie cheese sold at a cheese store is given by Upper P prime (x )equals x (60 x squared plus 90 x )comma where x is the amount of cheese​ sold, in hundreds of pounds. The​ "profit" is minus​$50 when no cheese is sold.
a. Find the profit function.
b. Find the profit from selling 400 pounds of Brie cheese.