Simple..
there is a major difference between 6z and \(z^{6}\)
6z means: 6 times z
and
\(z^{6}\) means: z to the power of 6(zzzzz*z)
An example...
make z=2...plug n chug..
6z----> 6(2)=12
and
\(z^{6}\)--->\(2^{6}\)=64
As you can see..there is a major difference.
Thus, your answer.