Complex sentence: In 2002 Gravingen and Romstad participated in starting up the Kitchen advertising agency, but in 2007 sold it to the international agency Leo Burnett Worldwide; it is now Leo Burnett Kitchen.
Split into simpler sentences: In 2002 Gravingen and Romstad participated in starting up the Kitchen advertising agency. It was sold in 2007 to the international agency Leo Burnett Worldwide and is now Leo Burnett Kitchen.