i will need to take a train to london kings cross on friday .
user
where are you departing from and when ?
assistant
i am departing from cambridge , preferably after 20:45
user
there are 2 trains that fit your criteria . 1 leaves at 21:00 and the other at 23:00 . which of these would you like me to book for you ?
assistant
i prefer the 21:00 please help me get the train id and price