JNXZ
      +---------
ZWNLL | QVGJWGZX
       -ZWNLL
        =====
        XYTQRG
       -XPTJMM
        ======
         GHUNVZ
        -LZJYWW
         ======
          RTZULX
         -RPXNVX
          ======
           LRVUH

base: 16
letters: GHJLMNPQRTUVWXYZ
difficulty: challenging