????????
      +---------
TJUQF | WQWYWTAJ
       -WJAUA
        =====
         QTATT
        -TJUQF
         =====
         UTTFAA
        -UTJFTF
         ======
           TJUWJ
          -TJUQF
           =====
           ?????

base: 10
letters: ACFJQRTUWY
missing: R C
hints: Y << R, R << C
difficulty: hard