I've been staring at this problem for a couple of hours now. It seems to me that a piece of information was left out of the book. But I guess I could be wrong.

Allan can drive his car over a route in 5 hours, and Carla can drive her car over the same route in 4 hours. How long would it take to meet if they started at opposite ends at the same time?

Can this problem be solved without a distance or rate?