?????????
      +----------
02390 | 3A5988412
       -02390
        =====
         86718
        -02390
         =====
         4A9514
        -443127
         ======
          623A41
         -692867
          ======
           928512
          -909B77
           ======
           ??????

base: 12
letters: 0123456789AB
difficulty: intermediate