A demand loan of $7000.00 is repaid by payments of $3500.00 after two years, $3500.00 after four years, and a final payment after eight years. Interest is 7% compounded quarterly for the first two years, 8% compounded monthly for the next two years, and 8% compounded semi-annually thereafter. What is the size of the final payment? The final payment is $ (Round the final answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.)