????????
      +---------
PJQRF | YLXTTMJL
       -PJQRF
        =====
        UWXQUM
       - PJQRF
        ======
         XGQGHJ
        -XYHLJT
         ======
          FTRRRL
         -UMLGGN
          ======
          ??????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard