The area is given by x( 2000 - 2x) where x is the width of the rectangular plot.
dA/dx = 2000 - 4x = 0 ( for maximum/ minimum area)
4x = 2000
x = 500
and the length of the plot = 2000- 2(500) = 1000
d^2y/dx^2 is negative so its a maximum area
Maximum area = 1000*500 = 500,000 m^2
