Average corporate bond and tax-exempt municipal bond rates were 9% and 6% respectively. 2. (a) At what marginal tax rate would an investor be indifferent between the two? (b) Helen has a marginal tax rate of 30%, which bond is more attractive to her? (c) Mark has a marginal tax rate of 40%, which bond is more attractive to him? (d) Based on your answers above, discuss why munis are popular among wealthy investors