Answer
The solution set is $\left\{-4, 4\right\}$.
Work Step by Step
Divide $5$ to both sides:
\begin{align*}
w^2&=16\end{align*}
Take the square root of both sides to obtain:
\begin{align*}
\sqrt{w^2}&=\pm\sqrt{16}\\
w&=\pm4\\
\end{align*}
Checking:
\begin{align*}
5(-4)^2&=80\\
5(16)&=80\\
80&\stackrel{\checkmark}=80
\end{align*}
\begin{align*}
5(4^2)&=80\\
5(16)&=80\\
80&\stackrel{\checkmark}=80
\end{align*}
Thus, the solution set is $\left\{-4, 4\right\}$.