So every 12dm

Footprints overlap once.

Every12m

There are four footprints.

Sange ningning

Two grandfathers'

One of them is coincidence.

So it's four (you can see it more clearly on paper)

So 60 footprints are

12*(60/4)=

180dm

The circumference is 18m.

2、4dm

Obviously.

3、 12dm

See 1 for the reason.

What grade is this?