Correct Answer - Option 1 : 16.10 hrs.
According to the given information,
The time of departure of next train = 18:00 hrs
As given the train for Patna leaves every two and a half hours from New Delhi Railway Station.
Thus time of departure of previous train = (18:00 - 2:30) hrs = 15:30 hrs
As the announcement was made at the station that the train for Patna had left 40 minutes ago means: (15:30 + 00:40) = 16:10 hrs
Hence, the correct answer is "16:10 hrs".