I would prefer to see the method return true or false versus Possible or Impossible as it seems more practical for a larger scale application. I would also drop "stations" from the required argument list.

I would swap lines 2 and 3 as there's no reason to convert to a string if you already know what you need to return; just edit your return to pass back the string.

Nearly 700 solutions has passed, so it is most likely your solution not doing exactly what is required.

You can post (as a comment) your current solution here and mark it as "Spoiler". Warriors already having solved the kata can then assist in pointing out what may be wrong (your code or the test code).

It may just be this example, or it may be codewars, but my code didn't pass the test validation (yet it passes on irb no problem). Seems that something is up with the compiler.