Hello! So, you use 120 pieces of fabric. You could not use all 120 pieces, because you can not make a square. The most you could use to make a square is 100. That would be 10 squares a row, with a side length of 6, which would make a perimeter of 60. Then, the other side would be 60. So 60 * 60 is 3600. The area of the blanket is 3600 square inches.
