Answer is
length =18 ft
Width = 7 ft
We know the area of the wall formula
A = length * width,
120 = (4 + 2x)x
120 = 4x + 2x²
2x² + 4x - 120 = 0
Divide by 2
x² + 2x - 60 = 0
x² + 8x - 6x - 60 = 0
x(x + 8) - 6(x + 10) = 0
(x - 6)(x + 10) (x + 8)= 0
By zero-product law, we know that:
Either, x - 6 = 0 ⇒ x = 6.
or, x + 10 = 0 ⇒ x = -10.
or x + 8 = 0 ⇒ x = -8
Since x is the width of the wall, it can not be negative. Thus we take x = 6.
∴ Width of the wall of the barn = 6 feet
Length of the wall of the barn =
4 + 2*6 = 4+ 12 = 18 feet.
Now we find the width by formula using length we found
2w + 4 = 18
2w = 14
w = 7