The formula for finding speed is distance divided by time:
Speed = Total Distance / Total Time
D1 = 50
TI = 4
D2 = 77
T2 = 3
Average speed = D1 + D2 / TI + T2
Average Speed = 50 + 77/ 4 + 3 = 127 / 7 = 18.14.
Therefore, the average speed of the train is 18.14 m/s.