Let the width = X
The length would be X + 20
Area = Length x width:
2400 = x * (x+20)
Simplify:
2400 = x^2 + 20x
Subtract 2400 from both sides:
x^2 + 20x - 2400 = 0
Factor:
(x-40) (x+60) = 0
Solve for both x's:
x = 40 and x = -60
The dimensions of a parking lot have to be positive values so you would use x = 40.
The width = x = 40
The length = x +20 = 40+20 = 60
The dimension of the parking lot is 40H x 60H