When solving for X the goal is to get it all by itself on one side of the equation and to do that you have to undo the operations already in effect on it. In number 9 the x is multiplied by 3 so to undo that you would need to divide by 3 and that would cancel out leaving the x by itself. Then you would need to divide by 3 on the other side of the equation also to keep it balenced. In number 10 the X is connected to the 10 through subtraction so to cancel that out you would subtract 10 from both sides to get the X alone.
I hope this helps and please don't hesitate to ask if there is anything still unclear!
