after tax WACC= what %

Capital Co. has a capital structure, based on current market values, that consists of 50 percent debt, 10 percent preferred stock, and 40 percent common stock. If the returns required by investors are 8 percent, 10 percent, and 15 percent for the debt, preferred stock, and common stock, respectively, what is Capital’s after-tax WACC? Assume that the firm’s marginal tax rate is 40 percent.