x(x + 2) = 120sq units
Set it equal to 0
x^2 + 2x - 120 = 0
factor
(x + 12)(x - 10)
For the shorter side:
x - 10 = 0
x = 10
Now that you have x, solve for the longer side which we said was represented by
x + 2
10 + 2 = 12
Proof
A = L x W
120 = 10 x 12
120 = 120
true
Our length is 12 and our width is 10