Answer:
1, 3, 4 are primary sources.
2, 5, 6 are secondary sources.
Explanation:
A primary source is a first-hand record, evidence or description about any person, thing or place.
A secondary source is a second-hand record that is obtained from a primary source.
1. A thank-you letter from a customer is a Primary Source.
2. A magazine about local companies is a Secondary Source.
3. A business report about sales -campaigns is a Primary Source.
4. A newspaper article is a Primary Source.
5. A person working at the same business is a Secondary Source.
6. A popular book about management styles is a Secondary Source.