Can you solve this Riddle?

2 boys on bicycles 20 miles apart begin racing towards each other. The instance they started a fly on the handlebar of one of the bikes started flying to the other bikes handlebar as soon as it reached it turned around and went to the other bike and so on until the bikes met I f each bike had a constant speed of 10mph, and the fly was travelling 15mph constantly, HOW FAR WILL THE FLY TRAVEL??