ASC Corporation issued $$25$ million $($par value$)$ of bonds to fund a capital expansion project. The bonds were $4\mathrm{.}4$ percent semiannual bond and currently sells for $104$ percent of its face value and has $15$ years to maturity. The company$$s tax rate is $32$ percent.

a$.$ What is the pretax cost of debt?b$.$ What is the after$-$tax cost of debt?c$.$ In addition to the $$25$ million bond issue, the company has a second debt issue on the market, a $3\mathrm{.}8$ percent semi$-$annual bond with $5$ years left to maturity; the book value of this issue is $$10$ million, and the bonds sell for $90$ percent of par. What is your best estimate of the after$-$tax cost of debt now? I am using excel spreadsheet and using RATE function and getting different answers! I a getting pre$-$tax cost of Debt for first bond as $4\mathrm{.}04\%$ and second bond as $6\mathrm{.}15\%$ and after tax cost of debt for first bond as $2\mathrm{.}75\%$ and second bond as $4\mathrm{.}18\%.$ Whay are we off?