????????
      +---------
LWBFB | LBNWURFF
       -LWBFB
        =====
         TBTTRF
        -TTNWRB
         ======
          WBWLBF
         -WNBFRX
          ======
          ??????

base: 10
letters: BFGLNRTUWX
difficulty: hard
missing: G