????????
      +---------
NUQHR | LRQRWRJF
       -NUQHR
        =====
        NYTPGR
       - TXNTH
        ======
         NJXGGJ
        -NJUPPM
         ======
           FNYGF
          -LQGJT
           =====
           ?????

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard