Chapter 15.5, Problem 20ES

Set up, but do not evaluate, an iterated integral equal to the given surface integral by projecting $\sigma$ on (a) the $xy\text{-plane},$ (b) the $xz\text{-plane},$ and (c) the $xz\text{-plane}\text{.}$

${\displaystyle \underset{\sigma }{\iint }xzdS,}$ where $\sigma$ is the portion of the sphere $x^2+y^2+z^2=a^2$ in the first octant.