l = length
w = width
l = w + 4
A = l * w
45 = (w+4) * w
45 = w^2 + 4w
0 = w^2 + 4w - 45
Use the factors of 45 to identify the missing coefficients.
45: 1, 45, 3, 15, 5, 9 (5 and 9 can give me 45 as the product and 4 as a difference.
(w + 9)(w - 5)
Thus if the length is 4 inches more than its width, the length = 9 inches and the width = 5 inches.