????????
      +---------
FXMUM | JRUXGRYU
       -JMMLG
        =====
         QPJWR
        -NGPRP
         =====
         FJJLTY
        -FMFUHF
         ======
          FUYQXU
         -FGGPLH
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: challenging