Asking for a solution to a specific puzzle seems to be on topic, but what tag should we use?
solutions is already used for both these types of questions and questions discussing solutions in general.
Also, as per the comment by TheDoctor, there are two kinds of puzzles to solve:
- Challenges set by a user to other users, and
- Puzzles that users need help on.
We need to keep in mind that a tag should be as specific as possible (IMHO, solutions is way too general since on a stack about puzzles, there will be a lot of solutions) while at the same time being intuitive enough that a new user will pick the right tag for the question, instead of using an inappropriate one that just looked right.