What we have
Every month the salesperson makes $2500
$325 for ever vehicle sold
We need to find out how he can make $5000 in a month
Solving
Knowing the first piece of information we automatically start off from $2500 and because we know each car is 325 we just need to add it onto it several times
2500+325+325+325+325+325+325+325+325 = 5100
Meaning above we will have an extra $100 no matter what we do
Counting the amount of "325's" I added we come to the total of 8
Answer
Meaning in order to earn $5000 in a month this sales person needs to sell 8 vehicles.