Assume that Marsha is indifferent between investing in a city of Destin bond that pays $4\mathrm{.}05$ percent interest and a corporate bond that pays $6\mathrm{.}05$ percent interest. What is Marsha's marginal tax rate?

Note: Do not round intermediate computations.

$66\mathrm{.}12$ percent

$48\mathrm{.}06$ percent

$38\mathrm{.}06$ percent

$24\mathrm{.}03$ percent

None of the choices are correct.