How can I solve these GHZ, 3 qubit quantum state problems?

[MattiaBosco]

TL;DR Summary: I have spent all day on these 2 problems but i cannot solve them. Can somebody give me any clue on the solution?

 

[PeterDonis]

Moderator's note: Thread moved to advanced physics homework forum.

@MattiaBosco please post whatever relevant equations you have and what attempts you have made at a solution.