Figure14-1Demand Schedule and Curve for Chocolate The rule for maximizing profit is to equate marginal revenue (MR) with marginal cost (MC). Here, the marginal cost is assumed to be zero. The profit-maximizing level of output under perfect competition is 120 million kilograms with a price of $0. Alternatively, if firms work together and act like a monopoly, they would set the price to $6 per kilogram and produce 60 million kilograms.