Two trains are traveling toward each other on parallel tracks
They start at the same time 300 miles apart
Train A is traveling east at 70 mph 
Train B is traveling west at 50 mph.

(a) How long will it take them to meet?
(b) How far will Train A have traveled when they meet?
(c) How far will Train B have traveled when they meet?

Make this chart.  The distance A goes until the meet and the
distance B goes before they meet is 300 miles total. The time 
till they meet is the same for both trains.  Let the time be t,
and put in their rates:

                distance     rate     time
faster train                  70        t
slower train                  50        t
total              300

Now use distance = rate × time to fill in the distances:


                distance     rate     time
faster train      70t         70        t
slower train      50t         50        t
total             300

The equation comes from 70t+50t = 300
                           120t = 300
                              t =  =  =  hours.

That's the answer to (a).

The answer to (b) is 70t or 70(5/2) = 175 miles.

The answer to (C) is 50t or 50(5/2) = 125 miles.

Edwn