The rise of is the most important music phenomenon of the second half of the 20th Centur

The rise of Rock-and-roll is the most important music phenomenon of the second half of the 20th century.

Ithink that'd be 4, sorry if i'm wrong.

This sounds like a personal reflection on something you did. it is asking the hardest part, or a part you may have struggled with on an informal interview you must have done. it is also asking advice you'd give someone else for the process of completing an informal interview, so you should write something that would . for example, maybe the first thing they should do, something they should include.