*** For this question, I have developed my own solution and sent it to the author of "Heard on Wall Street". Hopefully it will appear in the latest version :D ***

- The keypoint is to find out the hidden relationship between space and time that most people may miss.

- We first denote different variables:
  d₁: the distance traveled by the escalator at the moment Fischer just arrived at the top.
  d₂: the distance traveled by the escalator at the moment Myron just arrived at the top.
  D: the distance shown on the escalator at any moment.
  v_F: the velocity of Fisher.
  v_M: the velocity of Myron.
- We know that when Myron has arrived at the top, the distance on the escalator is:

d₁+25 = D
- When Fisher has reached the top:
d₂+20 = D
- Thus, we know the distance the escalator has travelled while Myron has stopped but Fischer walks is:
d' = 5   ***Why?: We just split the distances into people's distances and escalator's distance. Fisher only walks 25 steps, and Myron only walks 20 steps. D is constant at any time, so the difference 5 steps can only be the difference between the distances of the escalator.

- At the same time, we know:
v_M : v_F = 3:2 d_M : d_F = 3:2, when the time t is the same d_F = ²⁄₃d_M - We know that Myron has travelled 25 km, so based on the ratio, the actual distance Fischer has walked after Myron has reached the final point is: 20 - 25 * ²⁄₃ = ¹⁰⁄₃ - The time that the escalator continues to move is the same as that of Fischer has walked after Myron, and their velocities are constant.

- The ratio of their total distances will be the same as the ratio of the distances they both move after Myron has stopped.
d' : ¹⁰⁄_{3 = d2 : 20} - We solve it, and get d₂ = 30.

- If d₂ = 30, D = 30+20 = 50 steps.
*** Note: I have written a simple code to generalize this problem. If you want to check, please click on this link:
https://github.com/Kexin996/brainteaser/blob/master/july9.py