????????
      +---------
XRXRN | UFRWEFML
       -XRXRN
        =====
        EXFFNF
       -EYTYFE
        ======
         FTNXWM
        - XRXRN
         ======
          XFTFXL
         -XTUFTE
          ======
          ??????

base: 12
letters: CEFLMNRTUWXY
difficulty: intermediate
hints: E << C
missing: C