Pupils like to use what they have learned to give priority to calculation, and generally work out questions by playing with assumptions. The small circle should overlap around the big circle, equal to the length of the small circle and then equal to the length of the big circle. However, according to the circumference of a circle, a small circle of 3.5 is equal to a big circle. We can know that after the small circle turns 3.5 times, although the length is equal, the electricity A is above the electricity B, so only by repeating it can the point A coincide with the point B. So after seven times, the small circle grows into a big circle and overlaps, plus two times around the big circle, which is nine times.

The explanation is complicated, but it is still clear.