Learn what this means:

5# | 024466788 
6# | 01223455567889 
7# | 04569 
8# | 379

The digits 5,6,7,8 on the left of the line are the tens digits, and the
digits to the right of the line are the ones digit.  So it means this list
of numbers (values):

50,52,54,54,56,56,57,58,58 
60,61,62,62,63,64,65,65,65,66,67,68,68,69 
70,74,75,76,79 
83,87,89

The class 6#, which is the numbers in the sixties, (from 60 thru 69), has
the most values in it.  

"Frequency" just answers the question "how many?". I count 14 in 6#. So the
frequency of the class with the most values is 14.

Edwin