If you divide each of the lengths by 3, thus giving you the one-third of the finishing size, you'll get 2 inches for the length and 3 inches for the width.
If dimensions is perimeter, you get 2+2+3+3=10
10 inches=Perimeter.
You could also add up the sides and divide them by 3.
6+6+9+9=30
30/3=10 inches
