You are in charge of the revenue management department at the Richardson's Days Out Hotel, which has a total of 200 rooms. Xpedia (a travel fare aggregator company) is offering to buy your rooms for Valentine's Day at a rate of $200. On the other hand, you can book the rooms through your own website (which is far less popular than Xpedia) at a rate of $300. The demand on your own website follows a normal distribution with mean 20 and standard deviation 5, and all the rooms that you did not sell to Xpedia nor booked through your website result unoccupied

How many rooms should you sell to Xpedia?