For the first piece of string that is 12 feet long, he could make two 6 foot pieces. For the second piece of string that is 18 feet long he could make two 9 foot pieces. Hope I could help! :D
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.
