Answer:
Writing a blog entry that describes a friend's birthday party: informal style.
Writing a comment on the mayor's blog asking for a repeal of the youth curfew: formal style.
Writing blog entries every day about your personal struggles and victories: informal style.
Step-by-step explanation:
Informal style can be used when writing something related to personal experiences and informal situations. Particularly, blogs about personal experiences, such as a friend's birthday party or a daily blog about personal struggles and victories. On the other hand, any text aimed at a more formal audience, such as the mayor's blog should use a formal style to be taken seriously.