Calculate the after-tax return of a(n) 8.13 percent, 20 -year, A-rated corporate bond for an investor in the 15 percent marginal tax bracket. Compare this yield to a(n) 6.35 percent, 20 -year, A-rated, tax-exempt municipal bond, and explain which alternative is better. Repeat the calculations and comparison for an investor in the 33 percent marginal tax bracket. The after-tax return of the 8.13%,20-year, A-rated corporate bond for an investor in the 15% marginal tax bracket is %. (Round to two decimal places.)