Question

if A={1,3,5,7,11,13,17,19,23} and B={3,5,7,11} and C={3,11,13,23} and D={1,5,11,17} find
A. C ∩ A ∩ D
B. A ∪(B ∩ C) ∪ D

Answer 1

∩ - intersection (get the similar elements under each set indicated)
∪ - union (simply combine the elements under each set indicated)

Got it? :D

Answer 2

As he said for intersection look for the common elements btw all of those sets C,A,D
union is easy just combine the all elements of all those set
i case an element(a number) repeats write only once!