Here speed of first train is slower than speed of second train. So if they catch up , the distance traveled will be same since they left the same station at different times.
But the time traveled will be different .
Let us say the two trains meet at time t ,
Distance = speed * time
Distance traveled by first train = 40 t
Since second train is leaving after three hours , so
Distance traveled by second train = 60(t-3)
As discussed earlier, distance traveled will be same, so
distributing 60 over t-3
t=9
So the second train will meet the first at 9 p.m.