Charge a single occupancy rate for a night in a room?

Hi there, I am wondering how to charge a single occupancy more than say a group? For example 1 person books a night in the room it should be €60 per night but if a couple books a room it should be €100 as the room rate is technically €50 per night so there is a supplement charge for single occupancy. Can anyone help with this as its critical for bookings and I cannot find how to do this. Thanks in advance