????????
      +---------
NQQJH | PFHJHNQL
       -NQQJH
        =====
        QUJYYN
       -QPPUGY
        ======
         RPMQNQ
        -RRWMMF
         ======
          QTFHTL
         -QPPUGY
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
missing: X