Answer:
5 ft
Explanation:
In order to find the missing side length, we need to take a look at what has been given to us.
From what I see, this shape looks like two rectangles connect at their ends.
What do we know about rectangles?
-Rectangles have 2 sets of sides that are equal length, totaling 4 sides.
So, let's say we know the length of the longest side of the tallest rectangle.
-That side length is 15ft.
Now, we know that the opposite side of that imaginary rectangle has to be of equal length of 15ft. But, only 10 ft are show...
Since we know that there are more than 10 ft we must subtract 10 ft from the 15 ft to get the side length marked as "?", or what should have been left at that side.
15ft - 10ft = 5ft