?????????
      +----------
878A0 | 405DAA4FA
       -BAA05
        =====
         4FADA
        -BAA05
         =====
         832AD4
        -83963C
         ======
           5981F
          -53CE3
           =====
            7EBFA
           -EA99D
            =====
            ?????

base: 16
letters: 0123456789ABCDEF
difficulty: medium