Using the edge lengths already given, I calculated the height of the right side of the irregular octagon by adding the heights on the left. Since they added to 9m, then I put 9 on the edge with a missing height. To find the missing length, I subtracted the quantity of 6+6 from 18 (you can also divide 18 by 3) to get 6. Now that I know all the lengths, I can add them to get the perimeter. Since 3+3+3+6+6+6+9+18, or (3*3)+(6*3)+9+18 is equal to 54, our answer is 54.