HI, I want to know how can I calculate after-tax return, and why the after-tax return for common stock and preferred stock remain the same with before-tax return?

What is the WACC for XYZ Company if the cost of capital for common stock, preferred stock, and debt is 14%, 9%, and 10%, respectively? Assume a 40% tax rate) Before-tax After-tax Common stock Preferred stock Debt Weight % 60% 10% 30% 100% Return 14% 9% 1 0% Return 14% 9% 6% Calculation 8.4% .9% 1 .8% This is the calculated WACC! 12-40