At a recent boat show, Nautica Bank was offering add$-$on interest installment boat loans for up to $5$ years with an APR of $16\mathrm{.}5\%.$ On new boats, a $20\%$ down payment was required. Scott Vaughn wanted to finance a $$85,000$ boat for $5$ years.

$($a$)$

What would be the finance charge on the loan $($in $$)?$

$

$($b$)$

What would be the monthly payment $($in $$)?($Round your answer to the nearest cent.$)$