Final answer:
In 1989, the number of people who were self-employed in the United States is difficult to determine without more specific data.
Step-by-step explanation:
In 1989, the number of people who were self-employed in the United States can be estimated based on the information provided. Slightly less than half of all workers were employed at large firms with more than 500 workers, and another 35% were employed at firms with fewer than 100 workers. This means that a smaller percentage of workers were self-employed or working in small non-employer businesses where they receive whatever they can earn. It is difficult to determine the exact number of self-employed individuals in 1989 without more specific data.