9514 1404 393
Answer:
A. 6
Explanation:
The wording "set A and set B" means you're interested in elements that belong only to both. In your diagram, that is Region II. There are 6 elements that belong to A and B.
AB = 6
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Additional comment
"A and B" is also called the "intersection" of the two sets: A ∩ B.
The number you have chosen is the number in Regions I, II, and III. That is the set of elements that belong to A or B. You have identified the "union" of the two sets: A ∪ B. (It might also be represented as A+B.)