Can you please help me answer this question? I have already calculated the first 2 and confirmed they are correct. I do not know how to calculate the aftertax cost of debt.

Shanken Corp. issued a 10-year, 6 percent semiannual bond 2 years ago. The bond currently sells for 95 percent of its face value. The book value of the debt issue is $55 million. In addition, the company has a second debt issue on the market, a zero coupon bond with 15 years left to maturity; the book value of this issue is $30 million and the bonds sell for 55 percent of par. The company's tax rate is 40 percent. What is the company's total book value of debt? (Do not round intermediate calculations and enter your answer in dollars, not millions of dollars, e.g., 1,234,567.) Total book value $ 8500000! What is the company's total market value of debt? (Do not round intermediate calculations and enter your answer in dollars, not millions of dollars, e.g., 1,234,567.) Total market value $ 68750001 What is your best estimate of the aftertax cost of debt? (Do not round intermediate calculations and enter your answer as a percent rounded to 2 decimal places, e.g., 32.16.) Cost of debt 5.57 %