Answer
$u=\pi x^2$
$y=3\tan{u}$
Work Step by Step
Working from the inside out:
Take $x$; square it and multiply it by $\pi\leftarrow$ "inner function."
Take $\pi x^2$; take the tangent of it and multiply it by $3\leftarrow$ "outer function."
$u=\pi x^2$
$y=3\tan{u}$
