This was really fun! I like math puzzles a lot and this was really challenging. The music fits the chill tone of the game very well and the animations and sound effects give a real sense of polish, despite the minimalistic style. My only feedback (more of a nitpick really) is that dragging and dropping the numbers gets tiring quickly, it'd be nice to be able to just click on the numbers and either remove them or append them to the solution. Oh, and keyboard support would be nice! Nice job!