Question

How did the radio companies such as NBC , whose actual broadcasts were free, make money

Answer 1

Ok think about his, what do tv programs and radio programs get interrupted by every few minuets 
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Answer 2

Answer:

Radio stations principally make money through publicity.

Explanation:

Radio stations' profits are made through different activities, but the biggest part of it comes from advertisement time, there are other ways for radio stations to make money, since they don't charge for the service they provide to the citizens, like Radio Special Events, Syndication of Popular Programs, and Selling Newscasts to other Radio Stations .