Sorry to say this but I think the question is asking you what event would make you feel as happy as billy, not anyone else.
It would be a subordinate cause, for it can't stand on its own. Think about it: Since early this morning. What happened since early morning? Since it doesn't provide that information, it wouldn't be able to be an independent cause.
Also, I don't believe that the sentence is grammatically correct :)
Answer:
The character for this type of novel must be a teenager, who deals with common problems at this age and who needs to solve them alone or with the help of a group of friends, but without the direct help of adults or parents.
Explanation:
If you want to write a novel that has a high school student as its target audience, you must create a protagonist with whom your audience can identify. In this case, it is important that this protagosnista is a teenager, since most high school students are teenagers. In addition, this protagonist must have problems common to adolescents, such as uncertainties about the future, love problems, disagreement with parents and family, difficulty in getting along, among others. These problems must be overcome by the protagonist himself, together with a small group of friends, but without the interference of adults, so that the public has a feeling of capacity and independence.
