Sandhill Co. has a capital structure, based on current market values, that consists of 25 percent debt, 19 percent preferred stock, and 56 percent common stock. It the returns required by investors are 8 percent, 12 percent, and 15 percent for the debt, preferred stock, and common stock, respectively, what is Sandhill's after tax WACC? Assume that the firm's marginal tax rate is 28 percent.