Answer
-2
Work Step by Step
$-\frac{\sqrt -64}{\sqrt -16}=-\frac{i\sqrt 64}{i\sqrt 16}=-\frac{i}{i}\times\frac{\sqrt 64}{\sqrt 16}=-1\times\sqrt \frac{64}{16}=-1\times\sqrt 4=-1\times2=-2$
We know that $\sqrt -1=i$, because $i^{2}=-1$.
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