3. A demand loan of $10,000 is repaid by payments of $5000 in one year, $6000 in four years, and a final payment in six years. Interest on the loan is at 10% per annum compounded quarterly during the first year, 8% per annum compounded semi-annually for the next three years and 7.5% per annum compounded annually for the remaining years. Determine the final payment