????????
      +---------
PXWMR | ERTXTXPY
       -YWWLP
        =====
         YXFLX
        -XTMPE
         =====
         PTFMUP
        -PLMWTW
         ======
          PTTXFY
         -PLMWTW
          ======
          ??????

base: 12
letters: CEFLMPRTUWXY
missing: C
difficulty: medium