30 seconds every 15 minutes.
The total time passed was 8 hours and 16 minutes. 16 minutes late meant that the trip normally takes 8 hours. over 8 hours 16 minutes were lost. 16min divided by 8 hours is 2 minutes per hour. 2 minutes is 120 seconds (2*60). there are four 15 minute intervals in an hour so 120/4= 30 seconds per every 15 minutes.
