696B
      +---------
66EA4 | 6AB7BBB8
       -66EA4
        =====
         2638B
        -97C8A
         =====
          56D5B
         -66EA4
          =====
           7C888
          -1043D
           =====
            B5C8

base: 15
letters: 0123456789ABCDE
difficulty: hard