I was able to calculate the debt to equity ratio but I am having much trouble figuring out how my professor came up with 6.5% for the cost of debt after tax. Please assist me in any way possible.

A firm has issued $20 million in long-term bonds that now have 10 years remaining until maturity. The bonds carry an 8% annual coupon and are selling in the market for $877.10. The firm also has $45 million in market value of common stock. For cost of capital purposes, what portion of the firm is debt financed and what is the after-tax cost of debt, if the tax rate is 35%?

Answer:28.05%, 6.5%