????????
      +---------
XGFXF | WYLGNYMR
       -XGFXF
        =====
        JTXMUY
       -JWFRWU
        ======
         MTQNMM
        -MWGNYY
         ======
          MXPTLR
         -MUQUQL
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
missing: H