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# The order of $[7]$ in $(Z_{9},+_{9})$ is

$\begin{array}{1 1}(1)9&(2)6\\(3)3&(4)1\end{array}$

$Z_9= \{[0],[1],[2],[3],[4],[5],[6],[7],[8]\}$
The identity element in $Z_9$ is $[0]$
ie $n=9$