is the length. is the time it takes to
walk on the stalled escalator. is the time it takes to
ride the moving escalator. is the time to walk up the moving
The walking speed of the person relative to the stalled escalator
is .The speed of the escalator relative to
the ground is . The speed of the walking person
relative to the ground on a moving escalator is .
But these three speeds are related: .
Combine all this:
Put in the numbers and get .