It is known that the side length of a square is ACM. If the side length of the square is reduced by 3cm, how many cm is the area reduced

It is known that the side length of a square is ACM. If the side length of the square is reduced by 3cm, how many cm is the area reduced

The area is reduced by a ^ 2 - (A-3) ^ 2 = 6a-9 square cm