A freight train takes 4.5 hours longer to make a 420-mile journey than a passenger train. If the passenger train averages 30 mph faster than the freight train, how long does it take the passenger train to make the trip?

My teacher says the answer is 6 hours, but how do you set up this equation? I am very confused and have my midterm exam soon, if you can, please show your steps!! Thanks so much!