Roo club is planning a party at a hotel and it needs to comm…

Roo club is planning a party at a hotel and it needs to commit to a number of slots upfront. The hotel charges $90 per committed slot. If fewer guests show up than the commitment, the unused slots are lost without any refund. In contrast, if more guests show up than the commitment, Roo needs to pay $120 per slot for those that exceed the initial commitment. Roo club plans to use newsvendor model to determine the optimal upfront commitment. What is the critical ratio (i.e., Cu/(Cu+Co)) for this problem?