Sorensen Systems Inc. is expected to pay a $2.50 dividend at year end (D1 = $2.50), the dividend is expected to grow at a constant rate of 5.50% a year, and the common stock currently sells for $87.50 a share. The before-tax cost of debt is 7.50%, and the tax rate is 25%. The target capital structure consists of 45% debt and 55% common equity. What is the company's WACC if all the equity used is from retained earnings? Do not round your intermediate calculations.

a. 6.85%

b. 5.98%

c. 6.99%

d. 7.21%

e. 7.13%