Say there is a rectangular garden and a wall needs to be raised on all sides of it. How long should the wall be? The answer is that it needs to be as long as the perimeter of the rectangular garden. If one side of the garden is 5 feet and the other is 10 feet, what is its perimeter? The answer is simply 5 5 x 10 = 50 feet.
So one would need to build a 50-feet wall in order to completely surround the garden.