Question 1097682

A freight train and a passenger train are in stations 540km apart. The freight train leaves the station at noon travelling at 60km/hr in the direction of the passenger train . One hour later, the passenger train leaves and heads towards the freight train at 90km/h. At what time will the two trains meet.

I know why one of the equation is 540 = 60x + 90y, but I don't understand why the other equation is x=y+1. Please help me understand.
<pre>First of all, it's obvious that you let "x" and "y" be the times that the freight and passenger trains took, respectively, to get to the catch-up point. 
Now, since the freight train left one hour before the passenger train, and therefore took 1 hour more than the passenger train, to get to the catch-up point,
the TIME equation formed is: Time taken by freight train = Time taken by passenger train, plus 1, OR
                                                       x = y + 1