That's just an abbreviation or shortcut for writing this 
unabbreviated list of 6+4+4+2+3+1 = 20:

$6 $6 $6 $6 $6 $6 
$10 $10 $10 $10 
$11 $11 $11 $11 
$14 $14
$19 $19 $19
$24   

The frequency just indicates how many of each number there are in
the whole unabbreviated list.  You could just add all 20 of those 
numbers and divide by 20 to find the mean. But its easier just to 
multiply each number by how many there are of that number and add 
them up:

cost x  frequency  =   
-----------------------------
 $6        6      $36 
$10        4      $40
$11        4      $44
$14        2      $28
$19        3      $57 
$24        1      $24
---------------------
totals    20     $229

                      $  1 1.4 5
So we just divide 2 0)$2 2 9.0 0 
                      2 0
                        2 9
                        2 0
                          9 0
                          8 0
                          1 0 0      
                          1 0 0
                              0

So the weighted mean is $11.45

Edwin