Refer to the diagram shown below.
x = the width of each rectangular fence
y = the length of each rectangular fence
The amount of fencing available is 180 yards, therefore
2x + 2y = 180
x + y = 90 (1)
The total fenced area is
A = 2xy (2)
From (1), obtain
y = 90 -x (3)
Substitute (3) into (2).
A = 2x(90 - x) = 180x - 2x²
To maximize A,
A'(x) = 180 - 4x = 0 => x = 180/4 = 45 yds
y = 90 -x = 45 yds
The largest total enclosed area is
A = 2*x*y = 2*45² = 4050 yd²
Answer: 4050 yd²