A firm wishes to explore the effect on its cost of capital of the rate at which the company pays taxes. the firms wishes to maintain a capital structure of 25% debt, 15% preferred stock, and 60% common stock. The cost of financing with retained earnings is 11%, the cost of preferred stock financing is 9%, and the before-tax cost of debt financing is 9%. Calculate the weighted average cost of capital (WACC) given a tax rate of 40%. whats the firm's WACC?