Change from rectangular to spherical coordinates.
(a) (4, 4, 0)
$\left(\rho, \theta, \phi\right) = \left(4\sqrt{2}, \frac{\pi}{2}, \frac{\pi}{4}\right)$
(b) (15, $-5\sqrt{3}$, 10)
$\left(\rho, \theta, \phi\right) = \left(20, \frac{5\pi}{6}, \frac{\pi}{3}\right)$