????????
      +---------
NYPMR | JNMGLMPP
       -RQHJG
        =====
         RGPPM
        -NYPMR
         =====
         NXTTYP
        -NGRLWG
         ======
          WFWQFP
         -WHWMQG
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium
missing: U