I need to book a train from Cambridge and Norwich on Wednesday and I need to be there at 15:30.
When would you like to leave by?
I don't care when I leave as long as I get there by 15:30.
There are 9 trains matching your query. Shall I book one?
Can I get the departure and travel time of the train arriving closest to 15:30?
The travel time is 79 minutes. 
And the departure time please? For the train that arrives closest to 15:30?
The departure time is 13:38 and it arrives at 14:55. Would you like me to book it for you?
No, thank you and that is all i needed.  
Thank you, have a nice day, goodbye.