Answer:
Consider the following calculations
Step-by-step explanation:
Answer a. 
 
To calculate the after-tax cost of debt, multiply the before-tax cost of debt by (1 - T). 
 
Answer b. 
 
Before-tax Cost of Debt = 12.50% 
 
After-tax Cost of Debt = 12.50% * (1 - 0.25) 
After-tax Cost of Debt = 9.38% 
 
Answer c. 
 
Face Value = $1,000 
Current Price = $1,329.55 
 
Annual Coupon Rate = 12.00% 
Annual Coupon = 12.00% * $1,000 
Annual Coupon = $120 
 
Time to Maturity = 15 years 
 
Let Annual YTM be i% 
 
$1,329.55 = $120 * PVIFA(i%, 15) + $1,000 * PVIF(i%, 15) 
 
Using financial calculator: 
N = 15 
PV = -1329.55 
PMT = 120 
FV = 1000 
 
I = 8.1213% 
 
Annual YTM = 8.1213% 
 
Before-tax Cost of Debt = 8.1213% 
After-tax Cost of Debt = 8.1213% * (1 - 0.25) 
After-tax Cost of Debt = 6.09%