vans = v, buses = b, students = s
8v + 8b =312s ...eqn 1
9v + 4b = 196s ...eqn 2
divide eqn 1 by 2
4v + 4b = 156s ...eqn 3
eqn 2 - eqn 3
5v = 40s
v = 8s
subst v = 8s in eqn 2
72s + 4b = 196 s
b = 31s
answer
each van holds 8 students and each bus holds 31 students