Calculate the flux of the vector field $E(x, y, z) = (0, 0, x)$ through the part of the ellipsoid
$4x^2 + 9y^2 + z^2 = 36$
where $z \ge 3$, $x \ge 0$, and $y \ge 0$.
(Hint: Use the parametrization $\Psi(r, \theta) = (3r \cos(\theta), 2r \sin(\theta), 6\sqrt{1 - r^2})$ with an appropriate domain.)
