Excellent Game
It must be hard writing games for young people, i.e., people who mistake subtleties for "errors". This is a very good puzzle game, it forces a kind of calculation based on unknowns and lots and lots of variables. There are a lot of subtleties in this game, and learning them, failing, and trying other methods is basically the point of the game. There is no "ideal" difficulty, but every game is "about" a certain form of calculation that it brings out. This is the moment when you "get" the game, this is what the game expresses.