A firm has determined the cost of each source of capital and optimal capital structure, which is composed of the following sources and target market value proportions: Target Market Source of Capital Proportions After-Tax Cost Long-term debt Preferred stock Common stock equity The weighted average cost of capital is 40% 6% 10 11 50 15 O a. 10.7 percent O b. 6 percent Oc 11 percent O d. 15 percent