I need to find a train to take me to stansted airport.  Can you help me?
I have many trains going to Stansted Airport.  What is your preferred departure and arrival time? 
the train should leave Cambridge on Tuesday and arrive by 21.30
TR8261 leaves cambridge Tuesday at 9:40 and arrives at stansted airport by 10:08. Would you like to buy a ticket?
Yes I'd like to book for 3 and get the reference number if I could.
Booking was successful, the total fee is 30.29 GBP payable at the station. Reference number is TXK6U7DG.