a. $f(\rho, \theta, \phi) = \rho cos\phi$,
$E = \bigg\lbrace (\rho, \theta, \phi)|0 \le \rho \le 2, 0 \le \theta \le \pi/2, 0 \le \phi \le \pi/4\bigg\rbrace$
b.
$$\int_0^{\pi/2}\int_0^{\pi/4}\int_0^{2cos\phi} \rho^3 cos\phi sen \phi d\rho d\phi d\theta = \frac{75\pi}{24}$$