The length of a rectangle is 4 inches more than its width. if the area of the rectangle is 45 sq. inches, what is the width?

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.