The error you made could be hard to notice but it was made. So let's put the equation up, 6x-(2x-9)=-31. Your error occurred when you didn;t distribute the negative sign for (2x-9), if you woud have distributed it then the equation would then be simplified into 6x-2x+9=31. You then add like terms and get 4x+9=31, subtract 9 on both sides and you'll get 4x=22. Divide 4 on both sides to isolate the variable and you get x=5.5
The outlier is the piece of data that does not fit the general data set. In this case, 46 is much higher than all of the other numbers. This is the outlier.