I need help answering this questions. finding the profit in dollars from the sale of x

The profit in dollars from the sale of x expensive watches is P(x) = 0.08x- - 2x + 7x0.8 0.8 - 5500 Find the marginal profit when (a) x= 100, (b) x= 1000, (c) x= 6000, and (d) x= 12,000. (a) When x = 100, the marginal profit is $. (Round to the nearest integer as needed.)