Answer:
10.77%
Explanation:
FV: $1000
PV: $845.87
PMT: $60
Nper: 40 = (25 years - 5 years ago)* 2 for semi-annual payment
We use excel to calculate semi-annual discount rate by formula Rate(Nper,PMT,-PV,FV)
= rate(40,$60,-$845.87,$1000) = 7.18%
⇒ annual rate = semi-annual rate * 2 = 7.18% * 2 = 14.36%
after-tax cost of debt = 14.36% * (1 - 25%) = 10.77%
Please see excel attached for the calculation