Coca Cola has an optimal capital structure that is 60% common equity, 30% debt, and 10% preferred stock. Coca Cola's cost of equity is 10%. Its cost of preferred equity is 5%, and its pretax cost of debt is 6%. If the corporate tax rate is 30%, what is the weighed average cost of capital

a 8.76%

b 7.76%

c 6.76%

d 5.76%