Question 11253
When setting up proportions you first need to set up what you know and what you dont. 

You know that 2 adults are needed for 15 students so start setting up the proportion as: 2 over 15

Now you need to find out what you dont know: how many adults are needed for 180 students. So set up the proportion like you started to, putting the adults to students. You should have 2 over 15 equals X over 180.
               

Now we need to start the math. First cross mulitply the two numbers that you are able to, which are 2 and 180. You should come up with 360. Now, you divide 360 by the lonely number, 15. You should get X=12. 12 teachers are needed.

When doing proportions always remember to set up what you already know to what you need to know.