I have recently been approached by a high school student who wants tutoring for using the program "Mathematica". They asked me what I, as a tutor, would charge, but I wasn't sure what a fair rate is. I've seen everything from $10 per hour to $50 per hour on the intarweb, but I'm guessing $50 per hour is too much for this scenario. I don't want to charge so much that they don't return, but I also don't want to charge so little that I don't make much money. How can I maximize my profits, without knowing ahead of time how dedicated they are to learning the program? How much should I charge?