Question 311479
Train A speed = 40 mph
Train B 48 mph

Train A is ahead of train B at the station by 15 minutes.( 1/4 hour)

By the time train B reaches the station train A has traveled 40 * 1/4 miles
=10 miles to a point say P.

Let the distance from point P to the point where train B overtakes train A be x
.
Train B travels  10 + x miles in the same time the train A travels x  miles

time taken by train A = x/40  hours
time taken by train B = x+10  / 48
.
x/40 = x+10 /48
48x= 40(x+10)
48x=40x +400
8x= 400
x= 50

time taken by train A t travel 50 miles = 50/40
=5/4 hours= 75 minutes
This is the same time taken by train B to cross train A 

Add 75 minutes to the time when Train B was at the station. You know what to do

That is the time train B catches up