Two horses approach each other along the same country road, one walking at 5.5 km/h and the other at 4.5 km/h. when the horses are 10 km apart, a horsefly leaves one horse and flies at 30 km/h to the other, no sooner does the fly reach that horse than it turns around and returns to the first horse. if the fly continues to fly back and forth between the approaching horses, how far has the fly flown when the horses meet?