Invite experts to come in and solve the math problems in the fifth grade of primary school.
The requirements of the topic are very important. For example, if a coin just returns to its original position, then the distance the center of the circle passes is the circumference of a rectangle.
(30+20)*2= 100
If the topic is that the coin wraps around a rectangle, you need to add the diameter of the coin, because after one week, it also includes the width of the coin itself, that is, the diameter.