There should be a code of some kind on there that tells the nature of your infraction. You'll need to go to the local government website or call them to find the correct amount. I got one of those a while back and was amazed at how difficult it was just to find out how much I owed.
Do what I did in college. Just place it on the windshield of another car and there is a decent chance they will pay it for you. Many people don't read very closely.