????????
      +---------
54672 | 94BB07B5
       -A62B9
        =====
         B8387
        -A62B9
         =====
         40CDBB
        -47BD99
         ======
          D61CC5
         -DD8EA4
          ======
          ??????

base: 15
letters: 0123456789ABCDE
difficulty: hard