At the end of the month #1: debt = 37200, total payment by now = 5000
At the end of the month #2: debt = 34316, total payment by now = 10000
At the end of the month #3: debt = 31345.48, total payment by now = 15000
At the end of the month #4: debt = 28285.8444, total payment by now = 20000
At the end of the month #5: debt = 25134.419732, total payment by now = 25000
At the end of the month #6: debt = 21888.45232396, total payment by now = 30000
At the end of the month #7: debt = 18545.105893679, total payment by now = 35000
At the end of the month #8: debt = 15101.459070489, total payment by now = 40000
At the end of the month #9: debt = 11554.502842604, total payment by now = 45000
At the end of the month #10: debt = 7901.137927882, total payment by now = 50000
At the end of the month #11: debt = 4138.1720657184, total payment by now = 55000
At the end of the month #12: debt = 262.31722768997, total payment by now = 60000
Eventually in the month #13 the boy has totally paid 61270.186744521