I was wondering if you could help me in finding a train to the airport. 
Sure.  Where will you be leaving from?
I will need to leave from Cambridge if that's ok
What day are you travelling?
On Wednesday. I need the train to arrive by 19:15.
I have a train that arrives earlier at 18:08 and one that arrives just before your specified time at 19:08.
I'd like to book 3 tickets on the train arriving at 19:08, please. And would it be possible to have a reference number for the booking?
OK, you have 3 tickets reserved on TR4447, departing Cambridge at 18:40, arriving Stansted at 19:08. Total fee is 30.29 GBP. Reference #5VRJSMSE. Will that be all today?
Yes, it will. Thanks so much. Have a nice day. 
You are very welcome.  Enjoy your day too.  Bye.