Answer:
future value is $4353.89
Explanation:
given data 
invested = $125 each month
time = 20 year 
rate of return = 12.5 %
federal and state income tax = 24% = 0.24
inflation rate = 3.8% = 0.038
to find out
future value (after-tax and after-inflation)
solution
first we find here real rate of return by given formula that is 
1+ real rate of return =  ...................1
   ...................1
so here nominal return rate is = 12.5% ( 1 - 24% ) = 9.5% = 0.095
so
1+ real rate of return = 
real rate of return = 0.05491
so real rate of return is 5.49%
so
future value formula is express as 
future value =  ............2
     ............2
put here value
future value =  
 
future value = 4353.89
so future value is $4353.89