Initial speed of the train = 7 m/s
Final speed of the train = 17 m/s
Change of speed of the train = (17 - 7) m/s
= 10 m/s
Time taken for the change of the speed of the train = 120 s
Then
Acceleration of the train = Change of speed of the train/Time taken for the change of speed
= 10/120 m/s^2
= 1/12 m/s^2
= 0.083 m/s^2
So the acceleration of the train is 1/12 meter per second square or 0.083 m/s^2. I hope this is the answer you were looking for.