The correct Option is : 3.
Given the corrected values for ∪ , ∩ , and ( ∪ ) ∪ , we can find the following:
A ∪ B = {2,3,5,6,15}
C ∩ D = {6,7,8,11,15,26}
(A ∪ C) ∪ D = {2,3,5,7,11,15,21,26}
Comparing these values with the options provided, Option 3 is correct.