Answer:
Ⓒ {1, 2, 3, 6, 9, 13, 14}
Explanation:
One way to find the union of two sets is to list all the elements of both sets in order, then delete any duplicates.
Here, joining the two sets gives ...
{1, 6, 2, 3, 14, 2, 9, 13, 1}
Putting these elements into numerical order, we have ...
{1, 1, 2, 2, 3, 6, 9, 13, 14}
I have highlighted the duplicates. Deleting those gives us the desired union of the two sets:
X ∪ Y = {1, 2, 3, 6, 9, 13, 14} . . . . . matches choice C