RHWM
      +---------
RHWJL | FWXYHJRM
       -RHWJL
        =====
         TFNYJ
        -UGLJP
         =====
          PHTXR
         -XLGMQ
          =====
          RYLTRM
         -RFFXFP
          ======
           RYYNR

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium