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

I was hoping it would be pretty easy for an experienced coder???????

I think this should do you:

HTML Code: 

Kyle123 how hard would it be to convert a spreadsheet like this one into an html based calculator? Ideally I'd like for each one to be a checkbox with values 0 or 1, but if the person has to actually change a 0 into a 1 using the keyboard that would be ok, too... is this a difficult thing to do? I have no knowledge of javascript--just html, css, and I can manipulate php but not actually write code...

(If it's a monster of a thing, don't put yourself through it, obviously, but if it's easy to do, or if there is a pattern that you could show me so I could do it myself... that would be wonderful!)