generate response: I'll take the earlier train. could you tell me the travel time, and at what time I will be arriving at London Liverpool street?. Intent: find_train. Slots: train-day=friday, train-departure=cambridge, train-destination=london liverpool street, train-leaveat=21:15
Response: Sure, the travel time is 88 minutes and you will arrive at 23:27. Would you like me to book the train for you?