To find the perimeter of a shape you add all the side lengths together.
Perimeter of A is 20cm because 7+7+3+3=20
Perimeter of B is 27cm because 9+8+10=27
Perimeter of C is 17cm because 6+6+5=17
Perimeter of D is 34cm because 10+10+4+4+3+3=34
On shape E there is one side length that we do not know. To find that do 8-3=5 because 5+3 would be the opposite side of the 8. Now do 5+8+8+4+12+3=40 cm which is the perimeter of shape E.
I hope this helps you have a good day