Question 966051
Main outer dimensions of the rectangle, x and y.  Two fence portions are of y, and four fence portions are of x, so the total fencing to be 240 meters,
{{{2x+4y=240}}}.


The area is {{{A=xy}}}, for the whole outer rectangle.


Simplified, the fence length equation is {{{x+2y=120}}} and then {{{x=120-2y}}}.


Substituting, 
{{{A=(120-2y)y}}}
But if you just want to find the MAXMIUM for A, then this will be in the exact middle of the roots.


Roots:  {{{y(120-2y)=A=0}}}
{{{y=0}}} or {{{120-2y=0}}}, {{{y=60}}};


The exact middle of 0 and 60 is 30.
{{{highlight(y=30)}}} for the maximum area.]


{{{x=120-2*30}}}
{{{x=120-60}}}
{{{highlight(x=60)}}} for the maximum area.


The maximum area is {{{60*30=highlight(1800)}}}.