Answer
$19.2\ AU$
Work Step by Step
Given \begin{equation}
a=\sqrt[3]{P^2}.
\end{equation} Find $a(84)$:
\begin{equation}
\begin{aligned}
a(84)&=\sqrt[3]{84^2}\\
&\approx 19.2.
\end{aligned}
\end{equation} The distance from the sun to Uranus is about $19.2\ AU$.
