OK, let's look at this systematically. Are you qualified? Do you have a license? Are the problems in your area of expertise or subject matter expertise? If yes, then the next question is how detailed are the problems? Are they PE problems? FE problems? The average PE problem is designed to be 6 minutes in length to solve. Assume that you can work 5 problems an hour, you make $50/hour. The question really is are these problems in your area of expertise? Do you really know the problems? If yes, then the answer is you should be able to make $50/hour. Big salary? dON'T Think so, however, if you have nothing else to do, $50/hour is not too bad to work problems and identify solutions.
On the other hand, if you have to do a lot of research and review, then only 2 problems an hour might be your completion rate---$20/hour, well, you have to decide that.
Again, the lawyer's answer comes into play, "It depends."