A pair of friends and a pair of "enemies" in each group of three.

[L831]

Hello! I'm attempting to solve this problem several days, but have no idea even how to approach it.

The problem itself:
There is a class. In each group of three students in the class there is a pair of friends and a pair of "enemies". Find the maximum number of students in the class.

I tried to play with combinatorics, to find numbers of pairs and triplets. Also there was an idea to assign 0 (enemies) or 1 (friends) to each pair and try to limit sums of pairs and triplets using this measure. Didn't work.
Could someone help?
Thanks!

 

[stapel]

There is a class. In each group of three students in the class there is a pair of friends and a pair of "enemies". Find the maximum number of students in the class.

Since you haven't shown your work, we cannot provide any assistance there. But I think they've already given you a complete answer here.