YQR
      +--------
NQNRT | WMYXQTX
       -JMUXW
        =====
        LWXWFT
       -LHYPTU
        ======
         QLYJRX
        -XPRWHX
         ======
          QTJWG

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: challenging
missing: G