The rule of 72. 6. Show in Excel that if $20,000 is invested at 6% compounded annually, then it will double in about 12 years. (Note: 12=72/6) year F 1 23456780 9 Calculate the future value as the function of the years and see in which year the investment is doubled. Evaluate the future value in Excel using the cells of the year column. Keep the interest rate constant. 7. Show in Excel that if $20,000 is invested for 4 years, then it will approximately double at 18% compounded annually (Note 18=72/4) interest rate F 1 234567800-2 10 11 12 Calculate the future value as the function of the interest rates and see at which rate the investment is doubled. Evaluate the future value in Excel using the cells of the interest rate column. Keep the year in the formula constant.