The passenger train will take 2.5 hours to catch the freight train.
Step-by-step explanation
Suppose, it will take 
 hours for the passenger train to catch the freight train.
As the passenger train leaves the station after 30 minutes or 
 hour , so the freight train will travel the same distance as the passenger train in 
 hours. 
Speed of the freight train is 60 mph and speed of the passenger train is 72 mph. 
As 
 , so the equation will be......

So, the passenger train will take 2.5 hours to catch the freight train.