When shrinking an image, the size of each side is shrunk by the scale factor. However the area is not shrunk by the same factor. Area is a squared measurement (when finding the area of a rectangle we take length x width; two measurements, so a squared answer), so the area will be shrunk by the scale factor squared; in this case the area is shrunk by 3² or 9. This means the new area would be 720/9 or 80 square inches.