Question 912126
Let 
U = {3, 4, 5, 6, 7, 8, 9}, 
A = {3, 4, 5, 6}, 
B = {3, 4, 7, 8}, and 
C = {5, 7, 9}. 

List all the members of the given set. (Enter your answers as a comma-separated list.) 

(A ∪ B) means everything that is in either of the sets

so,(A ∪ B)= {3, 4, 5, 6} ∪ {3, 4, 7, 8}= {3,4,5,6,7,8}
 
then  (A ∪ B) ∩ C only the things that are in both of the sets


(A ∪ B) ∩ C ={3,4,5,6,7,8} ∩ {5, 7, 9} = {5,7}