????????
      +---------
TQFCU | EXHQXTUF
       -RRRFX
        =====
         NQUXT
        -TQFCU
         =====
         TXXHHU
        - QRTRU
         ======
           CFQXF
          -TQFCU
           =====
           ?????

base: 10
letters: CEFHNQRTUX
difficulty: easy