The Bartholomew Company's profit is related in the following way to its output: = 40

The Bartholomew Company's profit is related in the following way to its output: π = − 40 + 20Q − 3Q2, where π is total profit and Q is output.
a. If the firm's output equals 8, what is its marginal profit?
b. Derive an equation relating the firm's marginal profit to its output.
c. What output maximizes the firm's profit?