An absent minded scientist walks on an escalator at a rate

Escalator questions tend to confuse people but the point to note here is that they are just like Boats and Streams questions. If you are going in the direction of the escalator, it is like going downstream and your effective speed will be your speed + escalator speed. When you are going against the escalator, it is like going upstream and your effective speed will be your speed - escalator speed. The total distance to be traveled is the total number of steps on the escalator.
Then, you can very easily make the equations made by Bunuel and Sarang above:
\(\frac{y}{x+4}=15 and \frac{y}{4-x}=45\)

You can take a couple of quick guesses to solve this and in most cases you will get your answer in a couple of guesses.
e.g. lets say if x = 1, y = 75 from 1st equation
but x = 1 gives y = 135 in 2nd equation. So x is not 1
If x = 2, y = 90, from 1st equation
x = 2 gives y = 90 in 2nd equation. So x = 2 and y = 90.
Fun fact about GMAT: They give you numbers that make your life easy but twist concepts to make you think.

Also, if I am not wrong, these are CAT questions. I have not seen such questions in OG/Test prep material that I have come across. Nevertheless, every question is good for practice if you have the time. If time is less, you would do better to focus on 'GMAT type' questions available in OG.