Find doesn't work in mathcad

if you evaluate a solve block using numeric evaluation (the "normal" =  ) you are forcing Mathcad to use numerical algorithms which require an initial guess value for the variable you are looking for, as VladimirN had shown.

If you evalute the solve block symbolically, no guess value is required:

But  I think that In your case a numerical evaluation is more appropriate anyway.

You may want to look up the chapter on "Solving" in the Mathcad help for more details.

You may also use the "root" command instead of a solve block with "find".  You can use "root" in two different flavors:

Either provide an appropriate range (in the example I used the range from 1 to 10^7)

or you again provide a guess value before using "root"

Why not solve it symbolically, to get an exact answer:

Success!
Luc