Conversation so far:
What did Casey Kasem have to do with the American Top 40?
Casey Kasem along with Don Bustany, Tom Rounds, and Ron Jacobs, launched the weekly radio program American Top 40. He was co-creator and the host of the show.
When did Casey Kasem, Don Bustany, Tom Rounds, and Ron Jacobs launch American Top 40?
Casey Kasem, Don Bustany, Tom Rounds, and Ron Jacobs launched American Top 40 on July 4, 1970.
What else happened with Casey Kasem during the time he launched American Top 40?
In 1983, Casey Kasem helped found the American Video Awards, an annual music video award show taped for distribution to television, which he also hosted and co-produced.
How long did American Top 40 run?
Casey Kasem launched American Top 40 on July 4, 1970 and left the show in 1988.

Question: How many viewers/listeners did the show have?
Self-contained rewrite: How many listeners did the show American Top 40 have?