Is there a place where I can find the answers for challenges and mini challenges for swift 3 apprentice 3?
There are not answers as such, it is more an individual challenge. So you can try to do the challenges, and you can post anything you are having trouble with here and someone will try to help you. The idea is that doing is a much better way to learn than just reading.
You can actually check out the mini exercises and challenges corresponding and associated playgrouds for each and every single chapter of the book itself. Please let me know if you need help with anything else after doing just that. Thanks you! :]