Answer
$$3\pi $$
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 $$ Flux =\iiint_{o} 3x \space dz \space dy \space dx\\=\int_{0}^{\pi/2}\int_{0}^{\pi/2}\int_{0}^{2} (3 \rho \sin \phi \space \cos \theta) \times (\rho^2 \sin \phi) \space d\rho \space \space d\phi \space d\theta\\= \int_{0}^{\pi/2}(3\pi \cos \theta) d\theta \\= 3\pi $$
