This is a rectangular field, it will have four fence in one direction, and two in the other.
The vertical lines here are the same length on each other, likewise of the horizontal line.We can calculate the length of the fence from them as:
4V + 2H= L
we also have three area added together come to 800:
3VH = 800
so, lets re-arrange that second equation
H=800/3V
And sub into the first:
4V + 1600/3V = L
Multiply through by 3V:
12V^2+1600= 3LV
Rearrange
12V^2 - 3LV+ 1600= 0
we have quadratic, lets take a look at discriminant with this quadratic
discriminant= b^2 - 4ac
discriminant= 9L^2 - 4*12*1600
discriminant= 9L^2 - 76800
the dicriminant must be positive so the following must be true
9L^2>=76800
L^2>=8533.33
L>=92.376
so 92.36 is answer
