Set up the proportion with the numbers on top equalling the cars and the numbers on the bottom representing the trucks.
![\frac{8}{36} = \frac{c}{9}](https://tex.z-dn.net/?f=%20%5Cfrac%7B8%7D%7B36%7D%20%3D%20%5Cfrac%7Bc%7D%7B9%7D%20)
c equals the number of unknown cars.
To solve the proportion, cross multiply (multiply 8 by 9 and 36 by c) and solve for c.
72 = 36c
Divide 36 from both sides to get the answer.
c = 2
If there are 9 trucks, there are 2 cars.
You can check this by dividing 2 by 9, and dividing 8 by 36. Since they both equal the same number, this answer is correct.
Hope this helps =)