????????
      +---------
7DA08 | 637B8BA3
       -7DA08
        =====
        D2725B
       -D4A264
        ======
         B7A88A
        -B7C920
         ======
           95A43
          -073A6
           =====
           ?????

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