????????
      +---------
0B58D | 5B7699AC
       -0B58D
        =====
        C99C69
       -C9A06D
        ======
          0246A
         -0B58D
          =====
           5AC3C
          -0B58D
           =====
           ?????

base: 14
letters: 0123456789ABCD
difficulty: medium
missing: 1