i need a train that leaves at 18:45 and goes to cambridge .
{'service': 'train', 'act': 'request', 'slot_name': 'depart', 'value': '?'} {'service': 'train', 'act': 'request', 'slot_name': 'day', 'value': '?'}
sure . where are you departing from and what day would you like to travel ?