An installment contract for the purchase of a car requires payments of $$268\mathrm{.}38$ at the end of each month for $3$ years. Interest is $5\%$ per annum compounded monthly.

$($a$)$ What is the amount financed?

$($b$)$ How much is the interest cost?

$($a$)$ The amount financed is $

$($Round the final' answer to the nearest cent as needed. Round all intermediate values to six decimal places as needed.$)$