The words "select and rank" mean "to produce an ordered list".


In simple terms, the order in the list is important (does matter).


Therefore, there are  12*11*10*9 different lists/ways Kristen can do it:


    - any of 12 at the first position;

    - any of 11 remaining at the second position,


         . . .    and so on   . . . 


(standard mantra).