I have seen variations of this a couple of times, but this particular case is quite blatant.
The questioner went from a somewhat reasonably sounding homework question to something that has no context and makes no sense at all.
I feel tempted to revert the question one or two versions back, and I would if it had not been the questioner himself that made the changes.
What should be done? Prod the questioner to edit it again, or simply revert it?
A user vandalizing their own question is common enough. After a question is posted, it's no longer "owned" by the person who posted it so there's no reason to treat an edit from OP different than an edit from someone else.
Once a question has been answered it should not be removed unless it's off-topic or breaks any other policy. Stack Exchange's goal is to create a repository of good questions, so the question is the asset here - not the user (I understand that the Corporate Overlords disagree these days, I guess marketing dollars and PR is more important to the business side).
In the future, just revert it. IMO, OP does not deserve any slack after such a move and will probably not come back until it's time for the next homework question anyway.
It's already been reverted. Nothing to see here.
