Question 825286
w = the width along perimeter which Glenn cuts.
The whole lawn area is 40*30 m^2.


The area cut, {{{4w^2+2(40-2w)+2(30-2w)}}}.


That area cut is half the lawn area.
Solve this equation:   {{{4w^2+2(40-2w)+2(30-2w)=40*30/2}}}


Continuing a bit:
{{{2w^2+(40-2w+30-2w)=20*30/2}}}
{{{2w^2+70-4w=60}}}
{{{2w^2-4w+60=0}}}
{{{w^2-2w+30=0}}} seems not factorable;
{{{w=(2+sqrt(4+4*30))/(2)}}}
{{{w=(2+sqrt(124))/2}}}
{{{w=(2+2*sqrt(30))/2}}}
{{{highlight(w=1+sqrt(30))}}}