What is the intersection of A and B?

a (4,8,12,16)
b (8,16,24)

Intersection of A and B is the set that contains elements that are present in both A and B.

So for a={4,8,12,16}, and b={8,16,24}
only 8 and 16 appear in both a and b, so
a∩b={8,16}.