The topic for a personal narrative should always.
a. contain important facts and statistics.
b. have a main idea and supporting details.
c. be based a broad topic so you have plenty to write about.
d. present a worthy topic about how to make the world a better place.

The answer is b.) have a main idea and supporting details.

It is a personal narrative stick with the main idea and have a lot of details to support your idea.

faulty parallelism is a construction in which two or more parts of a sentence are equivalent in meaning but not grammatically similar in form.

the correct version of this faulty parallelism in the sentence is:

the hikers knew that the hike was six miles, that it usually required the entire day, and it would not be wise to start after 10: 00 a.m.

the problem is the last sentence, the first two have a basic subject+verb+object structure.

so, to give a proper balance to the structure, or better said, to give a parallel structure, we must write a basic s+v+o structure in all three sentences:

the hikers knew that the hike was six miles, that it usually required the entire day, and it would not be wise to start after 10: 00 a.m.