????????
      +---------
VMPYU | YGXQTHUJ
       -VMPYU
        =====
         NTHYH
        -UHPNX
         =====
          WYHWU
         -HTLQM
          =====
           HRMTJ
          -HTLQM
           =====
           ?????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: medium
hints: Z << P
missing: Z