Question

What am I supposed to put as an answer?? this is so confusing

Answer 1

The 'i' should go in front of the square root, not inside it.

So the answer should be $i\sqrt{15}$

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The way they wrote the expression $\sqrt{15}i$ is bit misleading as it might imply that the 'i' is under the square root. However the square root ends after the "5". It might be better to say $(\sqrt{15})i$ so there is clearer separation. But sticking the "i" in front is also a valid option.

side note: the plus minus part is already handled so there's no need to worry about that.