A company has determined that its optimal capital structure consists of 30 percent debt, 60 percent equity and 10 percent preferred stock. Given the following information, calculate the firm's weighted average cost of capital. Kd = 6% Tax rate = 40% Ks = 8% Kps = 10%

a. 6.0%

b. 6.2%

c. 6.9%

d. 7.2%

e. 8.0%