According to this article
https://docs.microsoft.com/en-us/windows/security/threat-protection/microsoft-defender-atp/machine-groups
- If a machine is also matched to other groups, it is added only to the highest ranked machine group. Part 1 answer should be - computer 1 will be a member of - Group 3 only.
Because its the highest rank and the machine is part of adatum.com Part 2 - if you add the tag demo to computer 1. then the answer should be group 1 only.
Because the machine is tagged "demo" and OS is windows 10.