????????
      +---------
A5D78 | A64C5BC3
       -A5D78
        =====
         059CB
        -B7044
         =====
         AAA48C
        -A26B1D
         ======
           08173
          -B7044
           =====
           ?????

base: 15
letters: 0123456789ABCDE
difficulty: hard
hints: E << D
missing: E