Answer:
10 inches
Explanation:
As you can see the perimeter is equal to 50 inches. This means that if you added up all the sides it would equal to that perimeter. In order to find the missing side, you would need to add all the sides that you know. This gives you 40 then subtract it from 50 which gives you 10.If you rather not do all the work its very noticeable that the side to the left of it is equal to it in size.