It is not correct. For sure it misses "for": Here comes an answer why FOR most of... Ans I would write it like this: Here comes an answer why form most of the teenagers... Or: Here comes an answer why for most teenagers... And it has sense: They are going to answer the question: "Why most teenagers do not feel motivated by health. Hope it is helpful.

Here comes an answer to why most teenagers' health is disheartening. It doesn't make a lot of sense though.