How do I solve this question? I do not understand how to do so.

The Goodsmith Charitable Foundation, which is tax-exempt, issued debt last year at 13 percent to help finance a new playground facility in Los Angeles. This year the cost of debt is 25 percent higher; that is, rms that paid 15 percent for debt last year will be paying 18.75 percent this year. a. If the Goodsmith Charitable Foundation borrowed money this year, what would the aftertax cost of debt be. based on their cost last year and the 25 percent increase? (Do not round intermediate calculations. Input your answer as a percent rounded to 2 decimal places.) Aftertax cost of debt % b. If the receipts of the foundation were found to be taxable by the IRS (at a rate of 35 percent because of involvement in political activities), what would the aftertax cost of debt be? (Do not round intermediate calculations. Input your answer as a percent rounded to 2 decimal places.) Aftertax cost of debt - %