Complex sentence: The airlines is based at Skien Airport, Geiteryggen, provides 21 weekly trips to Bergen, 10 weekly trips to Stavanger, and 4 weekly trips to Stockholm.
Split into simpler sentences: The airlines is based at Skien Airport, Geiteryggen. It provides 21 weekly trips to Bergen, 10 weekly trips to Stavanger, and 4 weekly trips to Stockholm.