Suppose a firm’s profit is given by the equation  = –200 + 80Q – .2Q2. Which of the following is true? a) The firm’s marginal profit is given by the equation: M = 80 – .2Q. b) The firm’s profit-maximizing output is Q = 400. c) The firm’s profit-maximizing output is Q = 200. d) The firm’s marginal profit is given by the equation: M = 80 – 2Q. e) The firm’s profit-maximizing output is Q = 800.