????????
      +---------
B3BC7 | 81930671
       -50A53
        =====
         88116
        -863D8
         =====
          DDB57
         -3439C
          =====
           88841
          -863D8
           =====
           ?????

base: 14
letters: 0123456789ABCD
difficulty: medium
missing: 2