????????
      +---------
QTMZG | MXUXQTNZ
       -QTMZG
        =====
        ZUHWXT
       - QTMZG
        ======
         YJXWZN
        -HXWJXP
         ======
          HZJJLZ
         -UQLPWR
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: hard
missing: V