FQP
       +---------
JEEXMQ | FMJMRNNX
        -FEYXQQ
         ======
          QQYYFN
         -QENPQN
          ======
           PQXQEX
          -PENJQF
           ======
            QJFJM

base: 10
letters: EFJMNPQRXY
difficulty: medium
restrictions: no multiplication