Complex sentence: He bought out the Cowles' brothers interest for $140,000 in 1950; during their 13-year partnership, the Cowles had earned nearly $1.8 million on their original $1,000 investment.
Split into simpler sentences: He bought out the Cowles brothers interest for $140,000 in 1950s. During their 13-year partnership, the Cowles had earned nearly $1.8 million on their original $1,000 investment.