2 vans = 12 students and 4 teachers
4 vans = 24 students and 8 teachers
6 vans = 36 students and 12 teachers
8 vans = 48 students and 16 teachers
Basically saying:
___ x 6 = 48
___ x 2 = 16
Since the answer to both of these equations is 8, then 8 vans are needed to carry 48 students and 16 teachers.
*If you need a better explanation of this process or have any questions or comments, you can ask me at any time, I'd be happy to help!