Complex sentence: The average circulation of the magazine was 70,000 copies in 1961, and it rose to over 120,000 copies in 1962 and 180,000 copies in 1973.
Split into simpler sentences: The average circulation of the magazine was 70,000 copies in 1961. It rose to over 120,000 copies in 1962 and 180,000 copies in 1973.