????????
      +---------
86A4B | B60AAB1A
       -B186B
        =====
         2B85B
        -86A4B
         =====
         837541
        -838652
         ======
           6118A
          -33527
           =====
           ?????

base: 12
letters: 0123456789AB
missing: 9
difficulty: medium