Answer
$3\pi$
Work Step by Step
As we know that $div F=\dfrac{\partial A}{\partial x}i+\dfrac{\partial B}{\partial y}j+\dfrac{\partial C}{\partial z}k$
Now, we have
$Flux =\iiint_{o} 3x dz dy dx$
Also,
$Flux =\nabla \cdot F=\int_{0}^{\pi/2}\int_{0}^{\pi/2}\int_{0}^{2} (3 \rho \sin \phi \cos \theta)(\rho^2 \sin \phi) d\rho d\phi d\theta$
This implies that
$\int_{0}^{\pi/2}(3\pi \cos \theta) d\theta = 3\pi$
