A rectangle is 14 cm long and 10 cm wide. If the length is reduced by x cms and its width is increased also by x cms so as to make it a square. Find the change in the area.

The answer is 4. The original area is 14 times 10 = 140, and since x should equal to 2 in order to make the rectangle square, the new area is 12 times 12 = 144. Therefore, the change in the area is 4.