Let `S` be the universal set, where:
`S = {1,2,3,...,18,19,20}`
Let sets `A` and `B` be subsets of `S`, where:

Set `A = \{ 1,3,7,8,9,11,15,17,19,20 }`

Set `B = \{ 4,7,9,10,13,14,15,16,17,18,20 }`

Find the following:

LIST the elements in the set (`A \cup B`):
`(A \cup B)` = { }
Enter the elements as a list, separated by commas. If the result is the empty set, enter DNE

LIST the elements in the set (`A \cap B`):
`(A \cap B)` = { }
Enter the elements as a list, separated by commas. If the result is the empty set, enter DNE

You may want to draw a Venn Diagram to help answer this question.

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