Answer:
on municipal bond after tax rate of return = 5 percent 
on corporate bond after tax rate of return = 5.44 percent 
Step-by-step explanation:
given data 
rates of return = 5% = 0.05
rates of return = 6.4% = 0.064
tax bracket = 15% = 0.15
solution
first we get on municipal bond yield
municipal bond is tax exempt so 
as on municipal bond there is no taxes is levied
so that here after tax rate of return will be as 5 percent 
and 
now we get after tax yield on corporate bond that is 
after tax rate of return = rates of return × ( 1 - tax bracket ) .............1
after tax rate of return = 6.4% × ( 1 - 15%) 
after tax rate of return = 0.064 × ( 1 - 0.15 ) 
after tax rate of return = 5.44 percent