????????
      +---------
CFRYJ | FRLYJLQR
       -FXJNJ
        =====
         RXEXL
        -CFRYJ
         =====
          WRQCQ
         -WCCQX
          =====
           CLFQR
          -CFRYJ
           =====
           ?????

base: 12
letters: CEFJLNQRUWXY
difficulty: medium
missing: U