Answer:
Pretax cost of debt is 8.58%
after tax cost of debt is 5.15%
After tax cost of debt of 5.15% is more relevant because that reflects the true cost of debt bearing in mind that debt has a tax advantage(tax shield).
Step-by-step explanation:
The pretax cost of debt can be computed using the rate formula in excel as follows:
=rate(nper,pmt,-pv,fv)
nper is the number of coupons the bond would pay i.e 25years(years to maturity)*2=50
pmt is the semiannual coupon interest=$1000*7.8%*6/12=$39
pv is the present price of the bond=$1000*92%=$920
fv is the face value of $1000
=rate(50,39,-920,1000)=4.29%
Annual yield=4.29%*2=8.58%
after tax cost of debt=pretax cost of debt*(1-t)
t is the tax rate of 40%
after tax cost of debt=8.58%*(1-0.4)=5.15%