A demand loan of ?$4000.00 is repaid by payments of ?$2000.00 after two ?years, ?$2000.00 after four ?years, and a final payment after seven years. Interest is 5?% compounded semi annually for the first two years, 6?% compounded quarterly for the next two years, and 6?% compounded semi annually thereafter. What is the size of the final? payment?