Thanks, for your  answer, however I guess I couldn't comunicate to  you my problem correctely .  I need to evaluate some  transcendental equations,  there the correct  anotation is k = ln(( M-m)/m(k-1)), as it's an equation. The equation is so as it is corrrect and evaluateable on maple as Back solver and comand line, solved and evaluated it for me. I can't change the annotion of k's that would change  the equation. My problem is in worksheet it dosen't evaluate. However after your tipp, I wrote the equation in function e.g 

f :=  x -> ln((M-m)/m(k-1)) ;
   
evalf(solve(f(x) = x, x));

This also could be solved. So as you know this is numerical appximation by Netown to Lambert W. So I would be happy to  evaluate this without puting it in function, as I have whole set of equations to solve. This is possible only I dont know why its not working on my laptop's Maple interface.

Thanks again

Thanks, for your  answer, however I guess I couldn't comunicate to  you my problem correctely .  I need to evaluate some  transcendental equations,  there the correct  anotation is k = ln(( M-m)/m(k-1)), as it's an equation. The equation is so as it is corrrect and evaluateable on maple as Back solver and comand line, solved and evaluated it for me. I can't change the annotion of k's that would change  the equation. My problem is in worksheet it dosen't evaluate. However after your tipp, I wrote the equation in function e.g 

f :=  x -> ln((M-m)/m(k-1)) ;
   
evalf(solve(f(x) = x, x));

This also could be solved. So as you know this is numerical appximation by Netown to Lambert W. So I would be happy to  evaluate this without puting it in function, as I have whole set of equations to solve. This is possible only I dont know why its not working on my laptop's Maple interface.

Thanks again