RTT
      +--------
RMQPH | QMMLJHG
       -FNMYX
        =====
        GNPMJH
       -GFUXFH
        ======
         GQTPXG
        -GFUXFH
         ======
          UHYWN

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