Well in one hour the train going east is going 40 mph. In 4 hours the train is 160miles because 40x4=160 so it's 160 miles away from the satiation, and train that's going west is going 50 mph. In 4 hours the train is 200 miles from the satiation. 50x4=200 if you add 160 and 200 you get the distance between both trains
