First write down explicitly what the elements of A and B are.A={15,20,25}, B={15,17,19,21,23,25}.

Remember ∪ means OR. So A ∪ B is the set of items which are in either A OR B. This is {15,17,19,21,23,25,15,20,25}.

Remember ∩ means AND. So A ∩ B is the set of items which are in both A AND B. This is {15,25}.