Tunis Carthage Airport is about 30 minutes from the Plaza Hotel.
Taxis are available right outside the arrival terminal. The travel to the hotel costs about 20DT. (10 Euros / 14 US$)
It's also possible to catch the Hotel Shuttle (free of charge). Reservation is mandatory at least 72 hours before arrival by calling the hotel (+216 71 808 948) or by email.