That key is on your keyboard. If you'll look just above the 
key that says ENTER you will find a key that types a backward 
slash \ and if you hold down the shift key and press it you 
will get a vertical bar |

|5x-3| - 3 = 9

First, Isolate the absolute value expression by adding 3
to both sides:

|5x-3| - 3 =  9
       + 3   +3
---------------
|5x-3|     = 12 

Now to remove the absolute value bars, make two equations:

5x-3 = 12    5x-3 = -12
  5x = 15      5x = -9 
   x = 3        x = 

There are usually (but not always) two solutions to an 
absolute value equation.

Edwin