Answer:
2
Explanation:
it starts out with 18 students, 24 pets in total. -16 for the dogs and cats, to lead up to 8, and 10 students left after subtracting 8 for how many students don't have a pet at home. So 2 students shouldn't have four legged pets left after subtracting the rest. (this is my answer, it's probably wrong, i think you should wait for more,)