Complex sentence: Jackson's financial interests in the music publishing business grew after he collaborated with Paul McCartney in the early 1980s and learned that McCartney was making approximately $40 million a year from other people's songs.
Split into simpler sentences: Jackson's financial interests in the music publishing business grew after Jackson collaborated with Paul McCartney in the early 1980s. He subsequently learned that McCartney was making approximately $40 million a year from other people's songs.