OK so each block is 3cm tall and 3.5cm wide (because 2 are 7cm wide)
so to measure the perimeter count all the side values for example:
the 5 squares at the bottom which measure 3.5cm each adds up to a total of 17.5cm then if you add the top 2 flat sides that's another 2, 3.5cm which adds up to 7cm. 17.5cm + 7cm = 24.5cm then their are 3 walls on each side measuring 3cm each so 3cm * 6 = 18
OK so each block is 3cm tall and 3.5cm wide (because 2 are 7cm wide)
so to measure the perimeter count all the side values for example:
the 5 squares at the bottom which measure 3.5cm each adds up to a total of 17.5cm then if you add the top 2 flat sides that's another 2, 3.5cm which adds up to 7cm. 17.5cm + 7cm = 24.5cm then their are 3 walls on each side measuring 3cm each so 3cm * 6 = 18
