Answer
$2 \pi$
Work Step by Step
Divergence Theorem: $\iiint_Ediv \overrightarrow{F}dV=\iint_S \overrightarrow{F}\cdot d\overrightarrow{S} $
where, $div F=\dfrac{\partial P}{\partial x}+\dfrac{\partial Q}{\partial y}+\dfrac{\partial R}{\partial z}=4 \sqrt {x^2+y^2+z^2}$
Consider the integral $I=(4) \int_{0}^{2 \pi}\int_0^{\pi/2} \int_{0}^{1} \sqrt {x^2+y^2+z^2} dV$
$=(4)\int_{0}^{2 \pi}\int_0^{\pi/2} \int_{0}^{1} \sqrt{\rho^2} \rho^2 \sin \phi \times d \rho d\phi d \theta$
$=(4) [\int_{0}^{2 \pi} d\theta] [\int_0^{\pi/2} \sin \phi d\phi] [\int_{0}^{1}[\rho^3 d \rho] $
$=(8 \pi) \times (-\cos \phi)_0^{\pi/2} \times [\dfrac{\rho^4}{4}]_0^1$
Hence, $I=2 \pi$
