Asecondary source comes from an eyewitness account

The rise of advertising in the 1920s. i am good with seeing how advertisements shape the roaring twenties and how it developed a new way of life through modern days. but i am not sure what the details of advertising in the 1920s were. if possible can you send me links (preferrably credential links) to sources that maybe show like the first company to start advertising through the radio, how advertising benefits (statistics graphs), etc.

Who was the first african american since reconstruction to be elected to congress from georgia?

Which piece of information would most a historian create an interpretation of this photograph of works in a factory?