Well, I won't often take a problem all the way to the end, for a few reasons-- I am not really supposed to be just doing your homework for you; rather, I'm trying to give you help with general approaches. I will typically get to the point where all the physics is done, and the rest is ``just algebra'' or ``just computation''-- for example, when you have enough equations and unknowns to solve the problem, or are ready to plug in numbers. This is the point at which, in an exam situation, you would get most of the points for the answer.
I don't feel it's most useful to spend much time in class doing computation, which I think most of you know how to do, and can sometimes be tedious. Of course, in some problems the algebra is tricky. If there is a problem you'd like to see it done for, please ask me in class to keep going, or come by office hours.