I want to know the whole process of calculation.

A mortgage pool is worth $10 million. Each mortgage has interest rate of 6%, term of 15 years and monthly payments based on full amortization. Mortgage servicing fee is an annual 1.2% of the mortgage balance charged on monthly basis as a percentage of the mortgage balance at the beginning of the month. What is the value marked by X? Beginning Required Expected Servicing Ending Month Balance Payment Interest Principal Prepayment Fee Balance 1 10.000.000 84,386 50.000 15,000 2 X 49,753 30,000 9,886,109 Selected Answer: D. 84,294 Correct Answer: C. 84,259