Define x:
Let x be the width of the border
Length of the rug = 15 -2x
Width of the rug = 12 -2x
Area of the rug = (15 - 2x)(12 - 2x)
Construct equation:
Given that the area of the rug os 108 ft²
(15 - 2x)(12 - 2x) = 108
Apply distributive property:
180 - 20x - 24x + 4x² = 108
Collect all terms on the left hand side:
4x² - 44x + 72 = 0
Factorise:
x² - 11x + 18 = 0
(x - 2) (x - 9)
Apply zero product property:
x = 2 or x = 9
Check x:
When x = 9,
Width = 12 - 9 - 9 = -6
⇒ x = 9 is rejected since width cannot be negative
When x = 2
Length = 15 - 2 - 2 = 11 ft
Width = 12 - 2 - 2 = 8 ft
Answer: The border is 2 feet wide.
