Calculate the future value of $6,000 in a. Four years at an interest rate of 9% per year. b. Eight years at an interest rate of 9% per year. c. Four years at an interest rate of 18% per year. d. Why is the amount of interest earned in part (a) less than half the amount of interest earned in part (b)? a. Four years at an interest rate of 9% per year. The future value of $6,000 in 4 years at an interest rate of 9% per year is $ (Round to the nearest dollar.)