Because he made a down payment of $3,000 he gets to subtract it out of the $7,500 that he needs to pay for the car.
$7,500 - $3,000= $4,500
In order to find out the monthly payments you need to devide the $4,500 by the number of payments.
$4,500/36= $125 <------ Answer
$125 =The monthly payments