A demand loan of $$8000\mathrm{.}00$ is repaid by payments of $$4000\mathrm{.}00$ after two years, $$4000\mathrm{.}00$ after four years, and a final payment after six years. Interest is $6\%$ compounded monthly for the first two years, $7\%$ compounded semi$-$annually for the next two years, and $7\%$ compounded annually thereafter. What is the size of the final payment?