Answer
$u=x^3-7.$
$y=\sqrt{u}.$
Work Step by Step
Working from the inside out:
Take $x$; cube it and then subtract $7$ from it $\leftarrow$ "inner function."
Take $x^3-7$; raise it to the power of $\dfrac{1}{2}\leftarrow$ "outer function."
$u=x^3-7.$
$y=\sqrt{u}.$
