Answer:
2 hours
Step-by-step explanation:
Given : The distance between New York City, NY, and Louisville, KY is 720 miles. One morning a train traveling 80 mph left from New York. Two hours later a slower train, traveling at 60 mph, left Louisville.
To find : How many hours will the slower train travel for before both trains will arrive at the same point?
Solution : Let the distance covered by NY is x
and let the distance covered by KY is y
Total distance covered is 
........[1]
→ New York city,
Distance traveled = x
Speed of the train = 80 mph
Time taken = t+2
Formula is 
.......[2]
→ Louisville,
Distance traveled = y
Speed of the train = 60 mph
Time taken = t
Formula is
.......[3]
Put the value of t from [3] into [2]
......[4]
Now, we solve equation [1] and [4],
Put the value of y from [1] and put back in [4], 
Put x=480 in [1]
So, The distance covered by train from New York city is x=480 miles
The distance covered by train from Louisville is y=240 miles.
Now put value of y in [3] to get time,
So, The time taken by train from Louisville is 4 hr.
The time taken by train from New York city is t+2=4+2=6 hr.
→ 6-4=2 hours will the slower train travel for before both trains will arrive at the same point.
