The game is very well polished (even to the title screen !) and feels nice to play or even just move the mouse around.
My only nitpick would be the difficulty (or lack of), since you can add / substract numbers between cards, and multiply / divide, I would expect to reach and/or make high numbers. having everything be <20 makes most puzzle trivial. Even more, what is the point of putting the goal of addition in behind a math equations ? This doesn’t tie much to the rest of the game/or design. Maybe have cards that are operands (+, x, /, etc..) that you could switch with the main equation and has such have greater design space ?
In any case, it is still an impressive game made in a short amount of time, congrats.