Neptune Corporation's bonds have 20-years to maturity and a coupon rate of 8.5%. Interest is paid semi-annually. The bonds sold at par value, but the firm paid flotation costs amounting to 4% of par value. The firm has a marginal tax rate of 21%. What is the firm's after-tax cost of debt for these bonds?

Group of answer choices

7.06%

6.72%

8.93%

8.5%

7.40%