Question 947326
Length, L;
Width, w;
p, perimeter;
-
{{{L=4w}}}.
{{{p=80}}}.
{{{2w+2L=p}}};
{{{2w+2L=80}}}
{{{highlight_green(2w+2(4w)=80)}}}


You can draw a diagram:
Draw a rectangle.  Label the longer dimension L, and label the shorter dimension w, and include with it, L=4w on the longer dimension.