You can read posting Sarin learns Perimeter, Area and Volume in school(Math Concept) to learn the concept of perimeter, area and volume.
Upper primary school mathematics question UPQ90
The diagram below is made up of three squares A, B and C. The area of square B is four times the area of square A. Find the length of square C.
Since the area of square B is four times the area of square A,
By divide the square B to four squares that same as square A in shape and size.
The length of square B = 3 + 3 = 6cm
The length of square C = 6 – 2 = 4cm