Question 357296
speed * time = dist
s=d/t
=d/20 escalator
=d/30 to walk up on the still escalator
.
s=d/20 + d/30
=3d/60 + 2d/60
=5d/60
.
t * 5d/60 = d
t = d * 60/5d
=12 seconds
.
Ed