Question 1183771
Draw this.
Long side is x and sum is 2x
Short side is y and sum is 3y, since there is an extra fence
We know that each short side fences is  (1/3) (900-2x) or 300-(2/3)x
the area is x*(300-(2/3)x)=300x-(2/3)x^2. This is f(x)

and that has to be maximized
the vertex for this negative quadratic is x=-b/2a or -300/(-4/3)=225 m
so the dimensions are 225 m x 150 m, and the area is 33750 m^2.
The length is 225 m and each width is 150 m