FYH
      +--------
QMPWN | MWHWNXP
       -UFYJN
        =====
        TYWFLX
       -TGJQFP
        ======
         TFTUJP
        -TTXPGL
         ======
          QQHQP

base: 15
letters: FGHJLMNPQRTUWXY
difficulty: hard
hints: Y << W, Y << X, P << U
missing: R