VenTek Corporation has a capital structure of 30% debt, 20% preferred stock, and 50% equity. The firms cost of equity is 10%, cost of preferred is 8%, and the after-tax cost of debt is 5%. What is the firms cost of capital? (hint: weighted average of the costs).

a) 7.5% b) 8.1% c) 8.4% d) 6.9% e) 8.0%