Lets call x how wide it is, and write the area equation:
area = width*length
a = (x)(x + 5) = 20000
expand it:
x^2 + 5x = 20000
make a quadratic trinomial:
x^2 + 5x - 20000 = 0
lets apply the general quadratic formula to solve:
x = (-5 +- √(25 + 80000))/2
x = (-5 +- 282.89)/2
we take the positive solution:
x = (-5 + 282.89)/2
x = 138.94
therefore the rectangle width is 138.94 m and 143.94 m long
