Convert Spreadsheet into a simple HTML/Flash/Javascript Calculator

I am wondering if someone would mind performing a real quick conversion for me? I want to create a simple calculator that I can upload to my website that will work the same way as my attached spreadsheet. I want to be able to input three of the four variables and have the calculator solve for the forth variable. The spreadsheet that I created works very well, but I do not want the answers generated in the C column to be visible if that variable is inputted by the user.

Hopefully I have expressed my desire clearly enough,
Zac