You start to ride your moped up a hill at a constant speed of 18mph.
One minute after you start, and every minute thereafter, a motorcycle starts the hill climb. The motorcycles all climb at the same speed, and one gets to the top at the same time as you.
At the top you turn around and go back down the hill twice as fast as you went up, arriving are the bottom just as a motorcycle starts up.
You notice that you met the same number of motorcycles on your decent as passed you on the way up.
How fast were the motorcycles going?