So you need us to help you find the math? you need to get help with code? You're looking for someone to code it for you or do you need advice of some other manner? Can you be a little more specific?
In general I suggest you:
1) First use pseudocode or a flowchart to map out what you want to do.
2) Next begin by working on small parts or modules of the program that you do know how to do.
3) When you get stuck, post some code example of what you have and we can more easily help you get past where you are stuck.
Remember - planning and design often takes more time than actual coding the applications. You can't just stare at the screen and start coding. Yes people like LizR could do this small app easily that way but even she couldn't do complex business programming that way and be efficient at it. So don't develop bad habits like trying to get the cart before the horse by coding without planning and design.
If you're already there, this message still applies to others who may read it. If that's the case, post what you're stuck on. (if it's stuck on where to start, have you written out the pseudocode yet? If you have then lets start by making sure it's correct. )
thank you very much for this information, I am really starting in the world of programming with c # and. net and this advice is very important to me. Do you have some interesting web site to learn how to analyze and plan and also to codify in c # and .net?