Question 893693
For a rectangle,
{{{A=L*W}}}
In this case,
{{{W=L-3}}}
Substituting,
{{{L*W=40}}}
{{{L(L-3)=40}}}
{{{L^2-3L=40}}}
{{{L^2-3L-40=0}}}
{{{(L-8)(L+5)=0}}}
Two solutions however only the positive solution makes sense here.
{{{L-8=0}}}
{{{L=8}}}{{{ft}}}
Then,
{{{W=8-3}}}
{{{W=5}}}{{{ft}}}