Bob invests 2000 at an effective annual interest rate of 15% for 10 years, Interest is payable annually and is reinvested at effective annual rate j. At the end of 10 accumulated interest is W. Mary invests 500 at the end of each year for 20 years at effective annual rate 12%. Interest is paid annually and reinvested at effective annual rate j. Let X be Mary's accumulated interest after 20 years. Express j as a function of X and W.