An office supply store sells about 60 graphing calculators per month for $100 each. For each $5 decrease in price, the store expects to sell 5 more calculators.

a. Write a quadratic function that represents the revenue from calculator sales. Let y represent the monthly revenue when there are x $5 price decreases. (Note: revenue = units sold × unit price)

b. How much should the store charge per calculator to maximize monthly revenue?

Please help me!!!

I know part b is 80 if that helps