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A debt of P100,000 is to be discharged by six (6) semi-annual payments, the first to be made 18 months after the loan is given. The debt will be discharged by 3 equal payments each of P20,000 and by 3 other equal payments of such amount that the final payment will liquidate the debt. If interest is 12% compounded semi-annually, what is the amount of the last 3 payments? If he was unable to pay 4th and 5th amortization, how much is the principal at the beginning of the 6th period?