Assume you get a job paying $70k per year. If you invest in the S&P 500 Index ETF or Mutual Fund, at the following percentages of your gross income, how much money will you accumulate in 20 years assuming the historical annual return of the S&P 500 Index(historical annual rate of 5.90%) ?

a. 10% per month of your gross income

b. 20% per month of your gross income

c. 30% per month of your gross income

d. 40% per month of your gross income