Can someone pls help me how to do this:(

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Explanation:

it might be just for me tho :(

Let

V the speed of the girl per step
v the speed of the escalator per step
L the length between ground and floor in number of steps

V*60+v*60=L => V+v=L/60
V*90-v*90=L => V-v=L/90

By adding the equations V+v=L/60 and V-v=L/90 we get:

2V=L(3+2)/180

V=5L/360

V = L/72

Time to climb (in steps) with v=0 (escalator standing still) is:

V*t=L

t = L/V

t = L/(L/72)

t =72 steps

The girl will count 72 steps.