QLN
      +--------
PTQTM | HMFHMPG
       -UWQNJ
        =====
         XGFNP
        -MLYPJ
         =====
         PMFUUG
        -PMNYTJ
         ======
           PUPW

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