Complex sentence: In 1950, after he sold his first cartoon to "The Saturday Evening Post", he worked as a freelance artist from 1950 to 1956, then spent a year-and-a-half doing television storyboards.
Split into simpler sentences: In 1950, he sold his first cartoon to "The Saturday Evening Post". After working as a freelance artist from 1950 to 1956, he spent a year-and-a-half doing television storyboards.