Return the booking start date and end date for the apartments that have type code "Duplex".
SELECT T1.booking_start_date ,  T1.booking_start_date FROM Apartment_Bookings AS T1 JOIN Apartments AS T2 ON T1.apt_id  =  T2.apt_id WHERE T2.apt_type_code  =  "Duplex"
booking start date and end date for apartments = T1.booking_start_date, T1.booking_end_date; apartments that have type code 'Duplex' refers to T2.apt_type_code = 'Duplex'; joining condition is on apartment ID = T1.apt_id = T2.apt_id;