An airport having AAA bond rating has issued 10-year municipal bond yielding 4.5%. A similarly rated corporate bond is yielding 5.5%. Suppose you have $10,000 available for investment. You dont know what will be your marginal tax rate in the coming years. Tabulate Municipal bond corporate bond yield spread (Municipal bond yield Corporate bond yield) for 10%, 15%, 25%, and 35 % marginal tax rates.

At what marginal tax rate would an investor be indifferent between buying airport bond and corporate bond?