Question 343237
freight train speed be x mph
express train speed = x+15 mph
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the express train leaves the station 1 hour later.

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express train travels 3(x+15)miles
freight train travels 4x miles
4x=3(x+15)
4x=3x+45
4x-3x=45
x=45 mph the speed of freight train.
speed of express train = x+15 = 60 mph