????????
      +---------
A6B04 | 1968B880
       -1BA44
        =====
         178B8
        -B58B4
         =====
         A64488
        -AA97B4
         ======
          A48680
         -A46504
          ======
           ?????

base: 12
letters: 0123456789AB
missing: 2 3
difficulty: hard
hints: 3 << 2