Math Is Fun Forum

I need help solving the following story problem?

Two trains 150 miles apart are traveling toward each other along the same track. The first train goes 60 miles per hour; the second train rushes along at 90 miles per hour. A fly is hovering just above the nose of the first train. It buzzes from the first train to the second train, turns around immediately (assume zero turnaround time), flies back to the first train, and turns around again. It goes on flying back and forth between the two trains until they collide. If the fly’s speed is 120 miles per hour, how far will it travel (answer is in miles).