To find perimeter, you add. In this, it gives you the perimeter, and you count the already given sides up, and you subtract that from the perimeter of the whole thing.
1. 12 cm
2. 4 ft
3. 20 mm
4. B
5. 15 yds because I added 10, 10 and 1 and then I got 21 and then I subtracted 36 - 21, and got the answer 15 yds
Glad I could help, and good luck!
