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Answer: A. 18</h3>
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Explanation:
The set A U B represents the list of items that are either in set A, set B or both sets at the same time. The "U" is the union symbol.
Set A U B looks like this
A U B = {-10, 8, 12, 26, 29, -8, - 1,5, 26, 36}
I basically started with set A, then tacked on the stuff in set B shown in bold.
From here, we toss out the duplicate item 26 and we can optionally sort the set
A U B = {-10, -8, -1, 5, 8, 12, 26, 29, 36}
We see that the number 18 is not in this final set, which is why choice A is the answer.
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Put another way: the number 18 is neither in set A nor set B, so it cannot be in set A U B.
Something like -10 is in set A, so it's going to be in set A U B as well. We can rule out choice B for this reason. Choices C and D follow a similar idea as choice B.
