Unlevering/relevering betas

2. Corrigan Inc. is trying to establish its optimal capital structure. Its current capital structure consists of 20% debt and 80% equity; however, the CEO believes the firm should use more debt. The risk-free rate, rRF, is 3%, the market risk premium, RPm, is 6%, and the firm's tax rate is 40%. Currently, the firm's cost of equity is 9.21%, which is determined by the CAPM. What would be the firm's estimated cost of equity if it changed its capital structure to 40% debt and 60% equity?

a. 8.40%

b. 9.36%

c. 9.75%

d. 10.00%

e. 10.56%