A new word problem I must have a mental block with these.

[mkay]

Two trains leave the same town at the same time going opposite directions.
The first train travels at 63 mph. The second travels at 75 mph. How many hours before they are 690 miles apart?

 

[tkhunny]

What have you done? Did you draw a picture?

Opposite directions - very important.

 

[HallsofIvy]

Each train has speed 63+ 75= 138 mph relative to the other.