I need a train leaving cambridge after 17:30.
Okay, is there somewhere specific you would like to travel to? 
I want to go to Stansted Airport on Saturday.
How many tickets would you like?
I am not sure yet, could you tel me how long the train takes to get there?
The train ride lasts 28 minutes. Would you like to book a ticket now?
No, thank you.
Ok, is there another train I can check for you?
No that is all thank you.
Okay don't hesitate to call us if you need further assistance.
Thank you for your assistance bye!
You are very welcome, goodbye.