Hoi Lee offers sightseeing boat trips in Sai Kung. Each of its 10 boats makes between 100 and 200 trips per month. The past data shows that a boat that makes 100 trips per month incurs an average operating cost of $350 per trip and one that makes 200 trips incurs an average operating cost of $300 per trip. Using operating cost of one boat and x is the number of trips during the month. Determine "b".

A. $10,000 per trip

B. None

C. 3,500 per trip

D. $6,000 per trip

E. $250 per trip