Complex sentence: Gerth began his career not in newspapers but in the marketing department of Standard Oil of Ohio; he was assigned to write down license plates of vehicles pulling in and out of gas stations to find out why drivers were choosing Standard Oil's rivals.
Split into simpler sentences: Gerth began his career not in newspapers but in the marketing department of Standard Oil of Ohio. He was assigned to write down license plates of vehicles pulling in and out of gas stations to find out why drivers were choosing Standard Oil's rivals.