Answer:
To sell the new 12-year unsecured debentures at par value, the coupon rate must be equal to the yield to maturity of the bonds, which is currently 5%.
To find the coupon rate for the new bond issue, we can use the following formula:
Coupon rate = Yield to maturity + [(Face value - Price) / (Face value x Years to maturity)]
Plugging in the numbers, we get:
Coupon rate = 5% + [(1000 - 1138) / (1000 x 12)]
Coupon rate = 5% + [-0.0118]
Coupon rate = 4.99%
Therefore, the coupon rate on the new 12-year unsecured debentures should be set at 4.99% to sell the bonds at their par value of $1000.