4. Mariano Manufacturing can issue a 25-year, 8.1% annual payment bond at par. Its investment bankers also stated that the company can sell an issue of annual payment preferred stock to corporate investors who are in the 40% tax bracket. The corporate investors require an after-tax return on the preferred that exceeds their after-tax return on the bonds by 1.6%, which would represent an after-tax risk premium. What coupon rate must be set on the preferred in order to issue it at par? a. 6.66% b. 6.99% c. 7.34% d. 7.71% e. 8.09%