Hi there!
One train is moving 55 towards the other one, which is moving at 65. If you add those up, you get a total of 120 miles per hour towards each other.
Remember that distance = rate*time.
Solving that for time:
time = distance/rate
time = 150/120
time = 1.25
1.25 hours (1 hour and 15 minutes)
Let me know if you have any questions. If not, thanks for pressing "Accept".
-Scott
MIT Graduate
College degree in math... proficient in all levels -- from algebra to calculus