Let the speed of the southbound train be x mph. then the speed of the northbound train will be x - 14 mph.
Both trains are traveling in the opposite direction and going away from each other.
The distance traveled by southbound train in 3 hours will be 3x miles. The distance traveled by southbound train will be 3(x - 14) miles.
Therefore, the sum of distance covered by both the trains will be equal to 498 miles.
Thus, the speed of the southbound train is 90 mph and the speed of the northbound train is 76 mph.