You have to find an equation that would relate the two motions of the locomotives. When they meet at a certain point after being 8.5 km apart initially, then that means that their individual distances traveled is equal to 8.5 The solution is as follows:
Distance = speed*time
Total distace = 8.5 = 155t + 155t
Solving for t,
t = 0.027 hour or 98.71 seconds
