please show the formulas

4. Your retirement account (which is expected to yield 8% return per year) has a current balance of $50,000. a. How much would you need to invest each year in order to accumulate a total of $1,000,000 in 20 years? b. If you decide to invest monthly, how much would you need to invest each month in order to accumulate a total of $1,000,000 in 20 years? C. Compare the annual investments in part (a) with the total amount that you would invest in one year in part (b) (12 times the monthly investments). Which one is greater? Why