Lexington's bonds have 15 years to maturity and a coupon rate of 7.5%. Interest is paid semi-annually. The bonds sold at par value, but the firm paid flotation costs amounting to 5% 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

5.93%

6.36%

4.04%

6.38%

7.5%