Answer:
The length (which is the bottom and top lines) are both 9 inches long.
Explanation:
To find the perimeter with only one given measurement and the total perimeter, first you need to double the given value. In this case it is 6 so 6 x 2 = 12. After that you need to find the rest of the sides so you can do 30 - 12 = x, or 12 + x = 30. As a total the answer is 18. Finally you divide 18 by two because there is two sides and you get 9.