Tail lining red star pattern

The relative distance that Teacher Wang walks back and forth is the length of the team.

The relative speed to the front is 150-60=90.

When reaching the tail, the relative speed is 150+60=2 10.

So the time ratio is s/90:s/2 10=7:3.

Go to the front row for 7 minutes and return for 3 minutes.

Team length s = 90 * 7 = 2 10 * 3 = 630m.