Well..., the goal is to get the x's (variables) on one side and the numbers on the other. So by subtracting 2x from both sides (we must always keep things equal and exact in mathematics- that is why you subtract from both sides of the equation) there are
no more x's left on the...

You cannot divide by 0 because there is nothing to divide. Zero is nothing. Think logically - if there are 12 pieces in a Hershey bar and you are divying it up between six kids, then each will have 2 pieces. Thereby leaving nothing (0) left should another
kid come and want some....