The buyer of Comparable A paid $$600,000$ for a house and took an $80\%,30-$year mortgage from the seller at an annual rate of $8\%.$ The market rate was $9\%.$ First, what is the amount of the loan to the nearest dollar? Second, what would have been the monthy payment on a market$-$rate mortgage to the nearest dollar? Third, what would be the monthly payment on the seller$-$financed $(8\%)$ mortgage to the nearest dollar?