The annual interest rate on a credit card is $16\mathrm{.}99\%.$ If a payment of $$100$ is $(10$ points$).$ Fony and Brian purchase a condo for $$161,250.$ After a $20\%$ down payment,

they sign a $20-$year mortgage at $7\mathrm{.}2\%$ compounded monthly.

$($a$)$ Find the monthly payment.

$($b$)$ After $5$ years, the net market value of the condo is $$200,000.$ How much equity in the

condo do they have after making $60$ monthly payments?made each month, how long will it take to pay off an unpaid balance of $$2,487\mathrm{.}56?$