Based on Exhibit $7-7,$ what would be the monthly mortgage payments for each of the following situations? $($Round your answers to $2$ decimal places.$)$

$\backslash$table$[[$a$.$ A $$161,500,15-$year loan at $6$ percent.,$],[$b$.$ A $$216,500,30-$year loan at $6\mathrm{.}5$ percent.,$],[$c$.$ A $$193,000,20-$year loan at $6\mathrm{.}5$ percent.,vdots