Question

Hello- Can I please have a mechanism and explanation for the following.

I understand that in the videos pertaining to this subject Johnny explained how H3O+ can have our sterodetermining carbon (C-5 usually) face up or down with the addition of H3O+. I also followed along with his lesson on hemiacetals, which was shown with the use of straight chains. Can I please see a mechanism of how to begin this problem then: enter image description here