van = v, bus = b, students = s
v + 6b = 372s ...eqn 1
4v + 12b = 780s ...eqn 2
divide eqn 2 by 4
v + 3b = 195s ...eqn 3
eqn 1 - eqn 3
3b = 177s
b = 59s
subst b = 59 in eqn 1
v + 354s = 372s
v = 18s
answer: each van holds 18 students and each bus holds 59 students