I have a problem to solve this equation
ln(m/(m-q*t))=g/u*t;
q,u,m and g are constants.
What sort of ideas or help are you expecting to get?
Perhaps if you posted the original question (complete with all instructions) which lead you to this equation as an answer, some progress might be made.
I suppose if you researched the Lambert W-function you might find what you're looking for ....