Ask a math problem: a square's side length is increased by 4cm, and its area is increased by 40cm RT

Ask a math problem: a square's side length is increased by 4cm, and its area is increased by 40cm RT

Let X be the original side length
(x+4)(x+4)-xx=40
xx+8x+16-xx=40
8x=24
x=3
Area = (3 + 4) (3 + 4) = 49 square centimeters