NTYL
      +---------
GTEUQ | UGEMRUGY
       -GTEUQ
        =====
        XNEQMU
       -XNTEXL
        ======
          TQEMGY
         -QEEUUL
          ======
           QEXLQ

base: 12
letters: CEGLMNQRTUXY
difficulty: intermediate
restrictions: no multiplication
missing: C