Answer:
I'm doing this for my school too, and I would show you a picture of mine so that you can easily copy it, but it won't let me access it.
It's kinda hard to explain.
Put the triangle with a 7 underneath the one with a 2 on it.
Put the square with an 8 underneath the one with a 3, and the one with a 12 under the 8.
Now put the diamond with a 9 under the 4, the 13 under the 9, and the 16 under the 13.
Hopefully you'll see the pattern at that point.