Calculate die after-tax cost of debt under each of the following conditions:
a. Interest rate of 13%, tax rate of 0%
b. Interest rate of 13%, tax rate of 20%
c. Interest rate of 13%, tax rate of 35%
a. Interest rate of 13%, tax rate of 0%
b. Interest rate of 13%, tax rate of 20%
c. Interest rate of 13%, tax rate of 35%