Let's call the width of the yard x and the length x + 3½. Since we know that perimeter = 2 * (width + length) and that the perimeter must be 26 we can write:
12 salads in 20 min divide both by 2 6 salads in 10 min divide by 2 3 salads in 5 min 20 min plus 20 min plus 5 min= 45 min 12+12+3=27 salads in 45 minutes