When you download a sample code project, you will see that each has a LICENSE folder. This is where the license is located for each sample code. From what I know, most of them, if not all, have MIT licenses, but make sure to check that yourself.
Regarding whether answering with "yes" to the submission form's field or not, here is a similar thread with an explanation on why giving credits is a good practice.
Good luck with your submission!
Topic:
Community
SubTopic:
Swift Student Challenge
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