Perimeter is the distance around an object.

Add the side lengths of the rectangle to find the perimeter.

5 feet + 10 feet + 5 feet + 10 feet = 30 feet

First, find the sum of the side lengths that are given.

5 feet + 10 feet + 5 feet = 20 feet

Then, subtract the sum from the perimeter.

24 feet - 20 feet = 4 feet

The length of the missing side is 4 feet.