MS Energy has a target capital structure of 30% debt, 10% preferred stock, and 60% common equity. The company's after-tax cost of debt is 5%, its cost of preferred stock is 8%, and its cost of retained earnings is 12%. What is the company's weighted average cost of capital if retained earnings are used to fund the common equity portion?
A. 8.0%
B. 9.50%
C. 10.20%
D. 12.80%.