In five minutes, boys arrive at the top left: 20×5= 100 (level), girls left: 15×5=75 (level).

Girls are in the back: 100-75=25 (level). At the last moment, the girl left 15, and the escalator left: 25-15= 10 (horizontal).

Escalator * * * is:10× 5+100 =150 (horizontal).