if say we have a widht of w, and its length is 4 times as long as w, then its length is 4*w or 4w.
[tex] \bf \textit{area of a rectangle}\\\\
A=Lw~~
\begin{cases}
L=4w\\
A=16
\end{cases}\implies 16=(4w)w\implies 16=4w^2
\\\\\\
\cfrac{16}{4}=w^2\implies 4=w^2\implies \sqrt{4}=w\implies \boxed{2=w}
\\\\[-0.35em]
\rule{34em}{0.25pt}\\\\
~\hfill \stackrel{perimeter}{\stackrel{L}{4(2)}+\stackrel{w}{2}\implies 10}\hfill [/tex]
