B. Applications 1. A firm's total cost function is TC = 6Q3 - 15Q2 + 30Q and demand is given by P = 50 - 6Q (i) Find expressions for the firm's average and marginal cost functions (ii) At what point is average cost equal to marginal cost? (iii) Sketch the firm's average and marginal cost curves on the same graph and comment on the economic significance of the relationship between them (iv) Find an expression for the firm's marginal revenue function (v ) At what point is marginal cost equal to marginal revenue? What is the economic significance of this point