You can read posting Sarin learns Perimeter, Area and Volume in school(Math Concept) to learn the concept of perimeter, area and volume.
Lower primary school mathematics question LPQ36
The perimeter of a rectangle is 7 times its breadth. If the perimeter of rectangle is 28 cm, find its length.
Breadth = 28 ÷ 7 = 4cm
Perimeter = breadth + breadth + length + length
Half of the perimeter = breadth + length
28 ÷ 2 = 4 + length
Length of the rectangle = 14 – 4 = 10cm