????????
      +---------
QJYVN | VHXMHXTQ
       -XNUUY
        =====
        QJYUZX
       -QVJYRT
        ======
         QNWWZT
        -QVJYRT
         ======
          QYJZRQ
         -QHLXXG
          ======
          ??????

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