Question 1050662
For a rectangle,
{{{A=L*W=108}}}
and,
{{{L=3+W}}}
Substituting,
{{{(3+W)W=108}}}
{{{W^2+3W=108}}}
{{{W^2+3W-108=0}}}
{{{(W+12)(W-9)=0}}}
Two solutions but only one is positive.
{{{W-9=0}}}
{{{W=9}}}{{{cm}}}
So then,
{{{L=108/9}}}
{{{L=12}}}{{{cm}}}