Train T starts at 3 PM and train S starts at 4 PM. Let the speed of train T be t. ⇒ Speed of train S=0.75t When the trains meet, train t would have traveled for one more hour than train S. Let us assume that the 2 trains meet x hours after 3 PM. Trains S would have traveled for x−1 hours. Distance traveled by train T=xt Distance traveled by train S=(x−1)*0.75t=0.75xt−0.75t We know that train T has traveled three fifths of the distance. Therefore, train S should have traveled two-fifths the distance between the 2 cities. ⇒(xt)/(0.75xt−0.75t)=3/2 2xt=2.25xt−2.25t 0.25x=2.25 x=9 hours. Train T takes 9 hours to cover three-fifths the distance. Therefore, to cover the entire distance, train T will take 9*(5/3)=15 hours. Therefore, 15 is the correct answer.train