@Alberth Good point, I have sometimes noticed that when someone does an operation (add or multiply), it can be hard to tell what happened, especially if you're learning the game. I think that could be mitigated if those operations were animated, but even then it might sometimes be unclear. A way to undo the last add/multiply operation might actually make sense, as long as there hasn't been any new tiles that have attached to the equation (which it seemed like you might not actually know about, if you've only started the tutorial and not played a real game).
Maybe a better way to teach the game would be start with a short video showing how a game works, then have people do the tutorial. The tutorial would then be to get familiar with the controls and different situations that can come up.