Hi. I'm an amateur student photographer who is studying photography. I have never sold photos, besides what photos of mine are used in the school paper. I shot some photos some time ago at a bike race that passed through our town and put them on flickr. Just recently, one of the sponsors of the racers contacted me and asked if they could use the photo in their marketing campaign. I really have no idea what to do from here and how this stuff works. How much should I charge? What's the next step? Any advice or things to watch out for? Thank you.