The perimeter of a rectangular line is 30cm. If the length and width are increased by 5cm, how many cm square will the area be increased

The perimeter of a rectangular line is 30cm. If the length and width are increased by 5cm, how many cm square will the area be increased

The added part can be divided into three parts
Two of them are small rectangles
The length of the two small rectangles is the length and width of the original rectangle
The width of these two small rectangles is 5cm
Another piece is a small square with a side length of 5cm
5*30/2+5*5=100cm2