Two trains are heading towards each other on a linear track

Two trains are heading towards each other on a linear track. One train travels at a speed of 60 miles per hour, and the other at 50 miles per hour. A fly starting at one train travels back and forth at a speed of 100 miles per hour. If the trains start 100 miles away from each other, how far will the fly travel before it is squashed by the collision?
Step through Step Answers would be prefered!

Solution

The trains approach each other at 110 mph (50 + 60)
It takes the trains 100/110 hours to meet.
The fly flies at 100 mph for 100/110 hours.
The fly\'s distance = 100*(100/110) miles
d =~ 90.91 miles