A free app for Android, by KosmoLizer.

Baldi is a popular online math game with hundreds of thousands of players around the world. He is also a popular math teacher for students who are studying algebra and calculus in university. But it is unacceptable to see him being killed! And the reason is not because he is an evil monster, but because his knowledge of algebra and calculus is so vast and deep that it is impossible to even imagine how much he knows about numbers and mathematics. And even if you are an expert in algebra and calculus, it is still impossible to solve his problems in your head. The only way to solve the problem is to get the notebooks he left behind. And you will need to collect them all before you can move on to the next level. And that is where the story begins.