A monopolist faces a demand curve P210 4Q and initially faces a constant marginal cost MC 10.

a) Calculate the profit-maximizing monopoly quantity and compute the monopolist's total revenue at the optimal price.

b) Suppose that the monopolist's marginal cost increases to MC 20. Verify that the monopolist's total revenue goes down.

c) Suppose that all firms in a perfectly competitive equilibrium had a constant marginal cost MC 10. Find the long-run perfectly competitive industry price and quantity.

d) Suppose that all firms' marginal costs increased to MC 20.Verify that the increase in marginal cost causes total industry revenue to go up.