How can I solve part (d) of this question?

Grady Zebrowski, age 25 , just graduated from college, accepted his first job with a $46,000 salary, and is already looking forward to retirement in 40 years. He assumes a 3.9 percent inflation rate and plans to live in retirement for 20 years. He does not want to plan on any Social Security benefits. Assume Grady can earn a 6 percent rate of return on his investments prior to retirement and a 7 percent rate of return on his investments post-retirement to answer the following questions using your financial calculator. a. Grady wants to replace 90 percent of his current net income. What is his annual need in today's dollars? b. Using the table , Grady thinks he might have an average tax rate of 13 percent at retirement if he is married. Adjusting for taxes, how much does Grady really need per year, in today's dollars? c. Adjusting for inflation, how much does Grady need per year in future dollars when he begins retirement in 40 years? d. If he needs this amount for 20 years, how much does he need in total for retirement? e. How much does Grady need to save per month to reach his retirement goal assuming he does not receive any employer match on his retirement savings? Click on the table icon to view the FVIF table. Click on the table icon to view the PVIFA table. Click on the table icon to view the FVIFA table a. Grady's annual need in today's dollars is $41,400. (Round to the nearest dollar.) b. Adjusting for taxes, the amount Grady needs per year, in today's dollars is $47,586. (Round to the nearest dollar.) c. Adjusting for inflation, the amount Grady needs per year in future dollars when he begins retirement in 40 years is (Round to the nearest dollar.) d. Since he needs this amount for 20 years, the total he needs for retirement is $ (Round to the nearest dollar.)