Complex sentence: In 2013, Clark co-wrote and produced Alex Hepburn's international hit single "Under", he co-wrote and co-produced Kim Cesarion's album, including the hit single "Undressed" which reached No.36 in the "Billboard" Hot 100.
Split into simpler sentences: In 2013, Clark co-wrote and produced Alex Hepburn's international hit single "Under". In the same year, Clark co-wrote and co-produced Kim Cesarion's album, "Undressed", including the eponymous single, "Undressed", which reached No.36 in the "Billboard" Hot 100.