Please answer A, B and C. Please show all work

P9-15 WACC and target weights After careful analysis, Dexter Brothers has determined that its optimal capital structure is composed of the sources and target market value weights shown in the following table. Source of capital Long-term debt Preferred stock Common stock equity Total Target market value weight 30% 1.5 55 100% The cost of debt is 4.2%, the cost of preferred stock is 9.5%, the cost of retained earn- ings is 13.0%, and the cost of new common stock is 15.0%. All are after-tax rates. The company's debt represents 25%, the preferred stock represents 10%, and the common stock equity represents 65% of total capital on the basis of the current mar- ket values of the three components. The company expects to have a significant amount of retained earnings available and does not expect to sell any new common stock. a. Calculate the WACC on the basis of historical market value weights. b. Calculate the WACC on the basis of target market value weights. c. Compare the answers obtained in parts a and b. Explain the differences