I feel like you may intend to wire the for loop iteration terminal to the index terminal of Replace Array Subset vi, but it doesn't influence the results anyway.
Is there a reason why the icon changes from the palette to the block diagram for some of the array functions but not others? In this case, Array subset is the same, the other three are different.
The given answers have different lengths, so you can also use that as an alternative way to find the correct answer. In each iteration two elements are deleted and then one added. 7-2+1-2+1=5 (after Insert in second iteration) and from that you take a subset which shortens the array by another element => The answer array has to be 4 elements long.
The Replace Array Subset is a red herring since it is just being deleted immediately afterwards.
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I think it is related to what you wire to the terminals. If you wire an array instead of just one constant, you would get a different icon for the first three vi