Jenny and Mark are throwing bottle caps. Jenny's bottlecap flies 18 feet straight, then bounces off a street light and flies another 1/3 of the distance it already went. Mark's bottle cap flies 15 feet forward, then bounces off a window and flies twice as far as it already did. How much further did Mark's bottle cap go than Jenny's?
Please reason step by step, and put your final answer within \boxed{}.
user