bool IDictionary <PassengerClassType, PassengerClass> .Remove(PassengerClassType key)
 {
     return(ClassDemand.Remove(key));
 }
 bool ICollection <KeyValuePair <PassengerClassType, PassengerClass> > .Remove(KeyValuePair <PassengerClassType, PassengerClass> item)
 {
     return(ClassDemand.Remove(item.Key));
 }