Answer: 20%
Step-by-step explanation:
Municipal Bonds are generally not taxed so if you invest in the Municipal bond, the tax rate does not affect you.
The tax rate therefore that will make you indifferent between the 2 options is the one that will take the Corporate bond returns of Jefferson to 8% so that both bonds may give you the same return after tax.
Assuming that tax rate is 'x' then,
8 = 10 (1 - x)
8 = 10 - 10x
10x = 10 - 8
10x = 2
x = 20%
At a tax rate of 20%, the Corporate bonds give an 8% return.