Robert Rhodes borrows $10,000 at an annual effective interest rate of 4% and agrees to repay it with installments at the end of each year for 30 years. The first 15 payments are each 2R, and the last 15 payments are each R. At the time of the 10th payment, Robert is given the option to repay the remainder of the loan with a final payment of X in addition to the regular payment then due. However, X is determined so that the lender will realize an annual effective interest rate of 4.5% over the entire 10-year investment period. Find X. (Answer: $6,879)