SOLUTION: Train A and B are traveling in the same direction on parellel tracks. Train A is traveling 80 miles per hour and train B is traveling at 88 miles per hour. Train A passes a station

Some teachers do not like for you to use approach-rate when one thing is
catching up to another, and separation rate when two things are going apart in
opposite directions.  But I will, because it's often easier. In fact using
approach rate, you can do this one in your head.

approach rate = the difference of the speeds
separation rate = sum of the speeds

This problem uses approach rate of 88-80 = 8 mph.  Here goes:

During the  hour (15 minutes) between 6:25PM and 6:40PM, train A has gone
 of 80 miles or 20 miles from the station.  So A has a 20 mile head start on
B at the time B leaves the station. Then B's approach rate is 88-80 or 8 miles
per hour.  Since time = distance/rate, it will take B  or  or  hours,  So 
2 and a half hours from 6:40PM will be 9:10PM.

Edwin