The installment payment terms are as follows:

$-$Selling price $25,000$

$-$Down payment$/$exchange car $6,000$

$-$Credit relationship establishment fee $120$

$-$The last installment is $25\%$ of the selling price

$-$Interest rate $6\mathrm{.}3\%$

$-$Billing fee $9/$month

$-$Credit period $32$ months

Calculate a$)$ installments $1-31$ and $32$ b$)$ credit price c$)$ credit costs