Question

How do I work this out?
Corporate bonds issued by Johnson Corporation currently yield 11%. Municipal bonds of equal risk currently yield 6.5%. At what tax rate would an investor be indifferent between these two bonds?

My answer is: 6.5%/1-11%=7.3
(7.3)(1- .11)=6.5

However, I keep getting this wrong and can not figure out the issue or how to solve this problem