TWO MISSILES speed directly toward each other, one at 9,000 miles per hour and
the other at 21,000 miles per hour. They start 1,317 miles apart. Without using
pencil and paper, calculate how far apart they are one minute before they collide.
The two missiles approach each other with combined speeds of 30,000 miles
per hour, or 500 miles per minute. By running the scene backward in time we
see that one minute before the collision the missiles would have to be 500 miles