Answer
$$-16$$
Work Step by Step
We know that $$ div F=\dfrac{\partial P}{\partial x}i+\dfrac{\partial Q}{\partial y}j $$
From the given equation, we have $ div F=-1-1=-2$
The volume of the cube is:
$$ div F=\iiint_R (-2) dA \\=(-2)[(2)(2)(2)] \\=-16$$
