Let the length of Gabby's backyard be denoted as \( x \) meters. According to the problem, the width is 4 meters shorter than the length, so we can express the width as \( x - 4 \) meters.
The area of a rectangle is given by the formula:
\[ \text{Area} = \text{Length} \times \text{Width} \]
Substituting the expressions we have for the length and width into this formula, we can set up the equation for the area:
\[ x(x - 4) = 120 \]
Now, this equation can be rearranged into a standard quadratic form:
\[ x^2 - 4x - 120 = 0 \]
This is the equation that can be used to find the possible values for the length \( x \) of Gabby’s backyard.