4551
      +---------
B66A8 | 07690740
       -B66A8
        =====
        AAC787
       -427B6A
        ======
         A3C964
        -427B6A
         ======
          33A220
         -521343
          ======
           37B91

base: 13
letters: 0123456789ABC
difficulty: medium
restrictions: no multiplication