The answer is 78 feet of fencing. This is because you need to find the perimeter of the yard. To find the perimeter of the yard, you add the sides together, so 21+21+18+18 = 78.
What you're doing here is you're trying to find the area of said area.
To find the area, just multiply 21 by 18 and you get 378.
Your answer could be... "<em>Gerrard needs 378 feet of fencing material. I found this answer out by finding the area. I multiplied 21 by 18 and in turn, I got 378!</em><em /> "
