Answer:
7:55 am
Step-by-step explanation:
To determine the time needed to leave, add up all of the elapsed time and subtract that from the 8:50 departure time. The 10 minutes from walking to the platform puts us at 8:40 am, 30 minutes to reach the station puts us at 8:10 am, and the extra 15 minutes gives a time of 7:55 am.