XYZ Corp Inc has two issues of debt outstanding.

One is a $9\%$ coupon bond with a face value of $$20$ million, a maturity of $10$ years, and yield to maturity of $10\%.$ Coupons are paid annually. The other bond issue has a maturity of $15$ years, with coupons also paid annually, and a coupon rate of $10\%.$ The face value of the issue is $$25$ million, and the issue sells for $94\%$ of par value. The firm$$s tax rate is $21\%.$

a$.$ What is the pretax cost of debt?

b$.$ What is the after$-$tax cost of debt?

please show me the calculations in excel and the formulas