????????
      +---------
17591 | 6356377D
       -76DA3
        =====
         B3D47
        -28B9A
         =====
          74BB7
         -31065
          =====
           8979D
          -D7430
           =====
           ?????

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