????????
      +---------
CC415 | A99A6E06
       -0DAA1
        =====
        22378E
       -280981
        ======
          62730
         -CC415
          =====
          843546
         -80B7E7
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: challenging
hints: 5 << A