a train leaves the station traveling west at 50 mph One hour

a train leaves the station traveling west at 50 mph. One hour later a second train leaves the station traveling west on the same track traveling 65 mph. How many hours will it take the second train to crash into the back of the first train

Solution

d=rt
d=50t
d=65(t-1)
50t=65(t-1)
50t=65t-65
50t-65t=-65
-15t=-65
t=-65/-15
t=13/3 or 4 1/3 hours after the first train leaves the station they will crash.
Proof:
50*13/3=65(13/3-1)
650/3=65(13/3-3/3)
650/3=65(10/3)
650/3=650/3