The correct answer to this open question is the following.
Who were the Robber Barons?
The Robber Barons were wealthy owners of the American Industries during the Gilde Edge. Two of the most famous Robber Barons were John F. Rockefeller, owner of the Standard Oil Company, and Andre Carnegie, owner of the Steel Company.
What positive impact did they have on the United States?
The positive impact was that they invested millions of dollars in developing their industries and the creation of thousands of jobs.
What challenges did the national economy face because of their existence?
The presence of their huge companies resulted in the lack of competition in their industries. They grew by buying other companies to the degree they became monopolies that dominated the industry.
What challenges did workers face because of their existence and how might those challenges be related to the rise of labor unions?
Workers labored for long hours a day and received low salaries. They also worked under unhealthy conditions that put them at risk. That is why they started to demand better working conditions and began to form labor unions.