Which primary source document would give you insight into how the great chicago fire affected working-class families? a.) a letter b.) a newspaper account c.) an essay d.) an immigrant newspaper

The answer is B. Because most likely the essay may not have all the info you need, and a letter is definitely not going to help, and the newspaper account may not have anything about the fire.

Primary sources are usually  more accurate and are written by someone who experienced it or witnessed it. secondary sources are those who heard of it after the fact that can lose details and or twist the event in a light that benefits them.