????????
      +---------
FB779 | 21628B11
       -D111A
        =====
        7EC07B
       - D111A
        ======
         FFB3D1
        -F73EE2
         ======
          783351
         -7CFCC2
          ======
          ??????

base: 16
letters: 0123456789ABCDEF
difficulty: medium
missing: 4