Consider a pool of $$100$ million in present value of $30-$year monthly mortgages. If the interest rate on each mortgage is $6\%,$ what is the payment that will be coming in for all of the mortgages? Divide the mortgages into $3$ tranches: $$25$ in tranche A$,$ $$50$ in tranche B$,$ and $$25$ in tranche C$.$ Tranche A has a coupon of $5\%,$ tranche B has a coupon of $5\mathrm{.}5\%,$ and tranche C has a coupon of $7\mathrm{.}5\%.$ Assume no prepayments, just regular amortization of the loans. Show the first $2$ months of payments. What is the remaining balance on tranche A after $2$ months of regular payments? Create an Excel spreadsheet.