Currently the length is 25 m, and the width is 20 m.
Both length and width will be increased by x.
The new length is 25 + x, and the new width is 20 + x.
The new area is 644.
The area of a rectangle is length * width.
L * W = 644
(x + 25)(x + 20) = 644
x^2 + 20x + 25x + 500 = 644
x^2 + 45x - 144 = 0
(x + 48)(x - 3) = 0
x + 48 = 0 or x - 3 = 0
x = -48 or x = 3
-48 cannot be the answer, so we discard x = -48
Answer: The width of the strip is 3 ft.
