Answer:
b. If a company's tax rate increases but the YTM on its noncallable bonds remains the same, the after-tax cost of its debt will fall.
Step-by-step explanation:
As we know that the cost of debt could be determined by applying the RATE formula in the excel
And, the following tax cost of debt is
= Cost of debt × (1 - tax tate)
In this case , the before the cost of debt or cost of debt remains constant but the tax rate is rising so automatically the following tax cost of debt would decrease
hence, the option b is correct