Complex sentence: At the end of 1956 she had another hit with "Jim Dandy" (number 1 R&B, number 17 pop), which sold over one million copies and was certified as a gold disc.
Split into simpler sentences: At the end of 1956 she had another smash hit with "Jim Dandy" (number 1 R&B, number 17 pop). It sold over one million copies and was certified as a gold disc.