Suppose our train left the station at 12 midnight. [every hour on the hour]....we would meet no train at that time because the other train would have had to have left at 7:30AM the previuos evening....but this is impossible because it would not have left "on the hour"
Instead, 15 minutes later [ at 12:15 AM].....we have met the train the left the other station at 8AM the previous evening [ and would arrive at our station of departure 15 minutes later....at 12:30 AM ]
Then......30 minutes later [ at 12:45 AM] we would meet the train that left at 9 AM the previous evening.......it has been traveling for 3 hrs, 45 min....and since we are 45 minutes from our station of departure......it's 45 min from its station of arrival......and it will arrive at 1:30 AM.....4 1/2 hours after its departure
Note the remaining patterns :
Our Time → Time that the train we meet left the station of departure [our station of arrival ]
1:15 AM → 10 PM
1:45 AM → 11AM
2:15 AM → 12 AM
2:45 AM → 1 AM
3:15 AM → 2 AM
3:45 AM → 3 AM
4:15 AM → 4 AM
Note that we don't meet any more trains after 4:15 AM.......we arrive at the station at 4:30AM, but the next train that departs that staion won't happen for 30 more minutes [ at 5 AM]
So....we pass a total of 9 trains......