$(8$ marks$)$: John has a fixed$-$rate mortgage of $500,000$ with rate j$2=5\%,$ amortized over $25$ years with monthly payment. The first term is $5$ years. Due to some special circumstance, John and the lender have agreed: one, John skips the regular payment that was supposed to be made at the end of $25$th month. This is the only payment missing. No more. Two, John makes a prepayment of $1,000$ at the end of $36$th month. The $1,000$ prepay made is well below the allowable limit$.$ So$,$ what is the mortgage outstanding balance at the end of first term?