first of all you must have a compound mitre box saw for this cut. If you have only a mitre box saw, then you can cope one side and mitre the other.
If you have a compound then I can give you the angles. You have to tell me how you want the crown positioned on the ceiling/wall intersection. In other words a reg 90degree or two 45 or something like a 50/40 or 60/30. This all means whether the crown sits higher on the ceiling or lower on the wall.