Equation solving with one unkown

Before it becomes a programming problem, I would first make it an algebra problem. As a quick review of the basic principles of solving simple linear equations like this: http://www.purplemath.com/modules/solvelin.htm Page 3 and 4 will be most interesting, as those are the pages where the examples begin to involve multiple instances of x.

I won't do it all for you, but I would start by getting the x out of the denominator by multiplying both sides by (0.0791-x). From there the algebra should be straightforward. Once the algebra is done, programming the resulting equation in Excel should be straightforward.

(13.621-x) / (7.91 / x) = 2.58

Multiply the right hand side produces
(13.62-x) = (7.91-x) * 2.58

13.62-x = 20.4078 -2.58x

Subtracting 13.62 from each side
-x = 6.7878 - 2.58x

Adding x to each side

6.7878 = 1.58x

So x = 6.7878 / 1.58 = 4.29 which is what you've said.

The answer's in here somewhere.

Originally Posted by Special-K

(13.621-x) / (7.91 / x) = 2.58

Multiply the right hand side produces
(13.62-x) = (7.91-x) * 2.58

13.62-x = 20.4078 -2.58x

Subtracting 13.62 from each side
-x = 6.7878 - 2.58x

Adding x to each side

6.7878 = 1.58x

So x = 6.7878 / 1.58 = 4.29 which is what you've said.

The answer's in here somewhere.

But Pelikan say, "How can do this in one excel formula?"