If a mastery challenge or practice exercise question isn't working correctly, it's best to notify Khan Academy using the Report a problem link in the lower right-hand corner of the page (see screenshot below). This allows the code ninjas on the back end to see exactly what problem you were working on and what steps you took when trying to solve it.
If the issue isn't specific to that one particular problem, please use the Report a problem button in the Help Center and send a Help request describing the steps you took and provide screenshots if possible.
Last updated September 26, 2017
Images updated September 26, 2017