A monopoly has a demand curve of D(p)=150-3P. If marginal cost is equal to 2, what is the profit maximizing quantity? Solution Q=150-3P i.e. the quantity demanded equation. The inverse demand function will be P = 50-Q/3 TR = PQ = 50Q - Q2/3 MR = 50 - 2Q/3 MC = 2 MR = MC 50 - 2Q/3=2 2Q/3 = 48 Q = 72 is the profit maximizing quantity..