MODELING WITH MATHEMATICS An office supply store sells about 80 graphing calculators per month for $120 each. For each $6 decrease in price, the store expects to sell eight more calculators. The revenue from calculator sales is given by the function R(n) = (unit price)(units
sold), or R(n) = (120 - 6n) (80 +8n), where n is the number of $6 price decreases.