Stumped by a homework question. At what point would an investor be indifferent between a Bridgford corporate bond yielding 8.

Stumped by a homework question. Could use some help.

At what point would an investor be indifferent between a Bridgford corporate bond yielding 8.0 percent and a tax-free municipal bond of equal financial strength if the investor's marginal tax rate is 25 percent?  (What would the equivilent Muni bond yield be at the point of indifference?)