I need to catch a train on Thursday, departing from Birmingham New Street.
Okay and what is your destination please?
I am travelling to Cambridge.
Please specify your choice of time for departure and arrival
I need to leave after 14:45.
What time do you need to arrive by?
I don't have an arrival preference.
I have the TR2148 that leaves at 15:40 for 75.10 pounds. Would you like to book it?
Yes I need 6 tickets and the reference number. 
Sure thing, I will work on that now and be back with you in a moment.