In anime we usually see highschoolers solving quadratic equations and learning basic chemical reactions. But that is just for show. A simple '2+2' would be uninteresting and they cant really show inequality graphs in pg-13 anime that young teens would find very difficult, so they stick to quadratics as they dont look too simple and not too complex either.
High schoolers DO solve quadratics, i am a highschooler too, but they arent as simple as shown in anime, they are wayy longer and complex.