Calculating the number of steps in an escalator

[viren_t2005]

There is a escalator and 12 persons move down it. A takes 50 steps and B takes 75 steps while the escalator is moving down.Given that the time taken by A to take 1 step is equal to time taken by B to take 3 steps. Find the no.of steps in the escalator while it is stationary

 

[vaishakh]

I think I am correct. Let x be the number of steps covered by A in the given time and let y be the steps escalator sailed. then
x + y = 50
3x + y = 75.
Thus we will get the answer y as to be 37.5