You can access other learners' published solutions by clicking Show solution. It costs 100 gems to see the reference solution for the projects and is completely free for the topics. You should be able to see the solution on the same page in the Solutions tab in the comment section.
Few things to keep in mind:
- This is available only in a limited number of topics and projects, and never for the last stage;
- This problem will not be added to your progress and to complete the topic you will need to solve an additional problem.