I also worked as a grader for Ordinary Differential Equations course (MATH 220), taught by Professor Van Vleck from the department of Mathematics at University of Kansas. Interestingly enough, one of my responsibilities was also typing up all the weekly homework solutions so that they can be used as "oracles", i.e. "source of truth" when grading students’ submissions.
This was quite an experience, because it has been a while since my intro ODE class. In a way, it felt like taking another courseload, as I had to type everything in LaTeX. Solutions are available both in the web form (rendered by KaTeX) and in PDF form (rendered with LaTeX). This might be a good source to catch up on your ODEs!