Answer
$$-3$$
Work Step by Step
Recall that the definition $\sqrt{-a} = i\sqrt{a}$ must be applied BEFORE the other rules regarding radicals, therefore,
$\frac{\sqrt{-12}*\sqrt{-6}}{\sqrt 8}$
$\frac{i\sqrt{12}*i\sqrt{6}}{\sqrt 8}$
$\frac{i^2\sqrt{72}}{\sqrt 8}$
$(i^2)(\sqrt{\frac{72}{8}})$
$(-1)(\sqrt 9)$
$$-3$$