Clay Harden borrowed $$21,000$ from a bank at an interest rate of $8\%$ compounded monthly. The loan will be repaid in $36$ equal monthly installments over three years. Immediately after his $19$th payment, Clay desires to pay the remainder of the loan in a single payment. Compute the total amount he must pay.

The total amount Clay must pay immediately after his $19$th payment will be $$.($Round to the nearest dollar.$)$