If demand is P = A bQ, then MR = A 2bQ. MC = dTC/dQ = c. The monopoly firm will profit-maximize by setting A 2bQ = c, so the equilibrium quantity traded will be Q* = (A-c)/2b. The profit-maximizing price will be given by substituting this into the demand curve, so P* = A b((A-c)/2b) = A A/2 + c/2 = A/2 + c/2 = (A + c)/2.