Question 902585
Let width = x.
Length = 12 + width
Length = 12 + x
width x length = area of rectangular garden
X x (12 + x) = 120
12x + {{{x^2}}} = 120


Completing the square:
{{{
  cartoon(
          Start,
          12x+x^2=120,
          x^2+12x=120,
          x^2+6x=120+36,
          x^2+6x=156,
          (x+6)^2=156,
          x+6=+-sqrt(156),
          TheEnd
         )
}}} ... Take note that the whole "PLUS_MINNUS-" is actually *[illustration .PNG]. Sorry because I can't type *[illustration .PNG] into the equation.

{{{x+6=sqrt(156)}}} or {{{x+6=-sqrt(156)}}}
{{{x=sqrt(156)-6}}} or {{{x=-sqrt(156)-6}}}
{{{x=6.49}}} or {{{x=-18.5}}}
{{{x=6.49}}} is acceptable, while {{{x=-18.5}}} is unacceptable since dimensions of an object cannot be in negative.


Dimensions of the rectangular garden:
Width = x = 6.49 ft
Length = 12 + x
Length = 12 + 6.49
Length = 18.49 ft