You are good at math, and operational research should not be difficult for you, mainly because of your mentality. Seriously, a large part of operational research is related to algebraic geometry, so your foundation is definitely ok. There is no question of who is difficult for these two. It depends on how you learn. In general, it is to fill in the blanks, choose and ask big questions. You can find several sets of questions you have tested before, which is very useful.