Although you can calculate the side length and perimeter from 64 square meters, there are no other figures, so you can't do this problem from the calculation point of view.

Consider mode 1

Calculate the side length from 64 square meters, and use a ruler to calculate the equal proportion (for example, if the calculated side length is 8 meters and the actual quantity is 8 centimeters, it will be calculated according to the ratio of 100: 1), or calculate the area ratio.

Consider mode 2

If the topic is not very rigorous, it is felt that the missing angle of the shadow accounts for about 1/9, and the missing angle accounts for 1/9 of the shadow.

64/9-(64/9* 1/9)