Answer:
(a) {-4, 2, 6, 9}
Explanation:
You want the domain of the function shown in the diagram.
Domain
The domain is the set of "input" values to the function. In this sort of diagram it is the set of values at the feet of the arrows.
The domain is {-4, 2, 6, 9}.
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Additional comment
When listing the elements of sets, it is customary to list them in order, with duplicates removed.