????????
      +---------
YRMMQ | MNWLZRVX
       -RYHHM
        =====
        XYXRRR
       -XTPWMG
        ======
         TGUUVV
        -TNGYYP
         ======
          TGRJPX
         -TNGYYP
          ======
          ??????

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: challenging