If it's academic study, then take a good look at the matrix theory in algebra and forget about abstract algebra. It's basically useless. Review the unary and multivariate calculus in analysis and see the limit. Real analysis (measurement theory) is generally not involved, unless you deliberately choose advanced courses, which are basically for reading.
Courses involving finance are generally difficult and teachers are strict. Except for advanced and finance, the rest of the basics are not too difficult. It is no problem to mix a B in the class honestly. It is suggested to look at time series, regression analysis, experimental design and multivariate statistics in advance, which are relatively basic (not to mention mathematical statistics). If possible, try to use r to solve the exercises yourself. The National University still attaches great importance to computer problem solving, and basically every course has to do projects.