Soon after the payment of the fortieth installment of a loan of $ 200,000.00 in 120 equal monthly installments, at the effective rate equal to 8.70%, you decide to amortize part of the outstanding balance at once, with an additional payment, in order to reduce by ten months the total term, in the same payment system, maintaining the interest rate and the value of the monthly payments. Calculate the percentage of the initial debt balance that must be amortized in this operation, that is, with this additional payment.