Complex sentence: In 2006 a number one single usually sold around 30,000 copies per week; sales of around 13,000 were often sufficient to reach the top ten, and a single selling over 2,500 copies could make the top forty.
Split into simpler sentences: In 2006 a number one single has usually sold around 30,000 copies per week. A single selling over 2,500 copies could make the top forty.