Step-by-step explanation: You are trying to get x by itself, and in order to do that, you need to get the 57 away from it. In order to do THAT, you need to do the opposite of what s already being done. Since your already subtracting it, in order to get it away from x, you need to add it to itself, and then add it to the other side, because what you do to one side, you do to one side, you must do to the other.
