Q:
An escalator is descending at constant speed.
A walks down and takes 50 steps to reach the bottom.
B runs down and takes 90 steps in the same time as A takes 10 steps.
how many steps are visible when the escalator is not operating.

hint from Hitequest:
S=50+Ve*T1
S=90+Ve*T2
50=V1*T1
90=V2*T2
10=V1*T2
Answer: S=100