So when Liang Da takes four steps and Dad takes three steps, there will be footprints overlapping, that is to say, there are only six out of seven footprints.

Now * * * has 60 footprints, so * * * should actually have 70 footprints.

40 of them are bright and 30 are dad's.

So the perimeter of the garden =40*54=2 160 cm.