I've tried searching for this but couldn't find anything that matched this problem.

I'm trying to figure out a way to enter in a single formula, one which has been solved for zero. And have excel solve for any variable that has been left blank.

So as a simple example take the equation "2X + 4Y - 8Z = 0"

I would like to enter this formula into excel and then fill in two of the variables and have it solve for the third. So if I enter values for X and Y it gives me a value for Z. Or if I give it values for X and Z, it gives Y. And if given Y and Z it solves for X.

Now this is a simple example, so I know it would be easy to rearrange the equation for each of the three variables and type all of them in to different cells. But the reason I would like to know if there's a way to do this is because I routinely deal with formula's that have 20 or more variables easily. I'd rather not have to rearrange that many times. It would be great to just solve for zero, plug that one equation in, have all my variables listed. Then whichever value i leave blank it solves for that unknown. As you can imagine with that many variables I've hesitated from even thinking about doing nested IF statements. I shudder at even trying to keep that straight.

Is there any way that this can be done automatically in excel?

And yes, i can do simple enough VBA (not a master of that, but I get by). So if that's an option I'd love to hear any ideas.