The appropriate formula is: D = R · T (distance = rate · time)
For the freight train: since it is traveling at 40 mph, rate = 40 ---> D = 40T
[D represents the distance that the freight train covers, T represents the time that it takes]
For the second train: traveling at 60 mph, rate = 60 and since it starts two hours later, time = T - 2
and since it covers the same distance as the freight train, its distance is also D ---> D = 60(T - 2)
Since the distance are equal, set the right-hand side of thetwo equations equal to each other:
40T = 60(T - 2)
40T = 60T - 120
-20T = -120
T = 6 hours (this is the time for the freight train)
T - 2 = 4 hours (this is the time for the second train) <-- the answer
{I hope that the trains are on separate, parallel tracks ...)