????????
      +---------
GMMJG | UFMGFXNW
       -GMMJG
        =====
        GNRXLX
       -XQMNJM
        ======
         XUJXYN
        -XGMNQT
         ======
          XFRHXW
         -XUTPRX
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: medium