You are analyzing the cost of debt for a firm. You know that the firm's $14$ year maturity, $7\mathrm{.}8\%$ coupon bonds are selling at a price of $$830\mathrm{.}00.$ The bonds pay interest semialnnually. If these bonds are the only debt outstanding for the firm, answer the following questions.

Current YTM for the bonds is $10\mathrm{.}09\%.$ Now what is the after$-$tax cost of debt for this firm if it is subject to $30\%$ marginal and average tax rates?

after$-$tax cost of debt?