Dr. smith gives his staff a 13 bonus if they exceed the quarterly goal. this quarter, they exceeded the goal by $1,500.

Here is what you have to take into account:
The first thing you need to do is to take the 1,500$ and then divide it by 3. That will give you 500. After that you need to add 500 to the original 1500 and it should give you 2000$. The answer is 500 if you only are looking for the bonus and 2000 if you want the total bonus.  

X=3 and y=4 is the answer