Answer
Length of rectangular garden = x feet
As, Width is 3 feet less than Length.
Width = (x-3 ) feet
Area of Rectangle = Length × Breadth
Area = 54 square feet
→54 = x × (x-3)
→ x²-3 x-54=0
Splitting the Middle term
→x² - 9 x + 6 x- 54=0
→x × (x-9)+6 × (x-9)=0
→ (x+6)(x-9)=0
→x+6=0 ∧ x-9=0
x≠-6, as length can't be negative.
So, x=9
Length of Rectangular garden = 9 feet