$[-/2\mathrm{.}22$ Points$]$

SCALCET$711\mathrm{.}8\mathrm{.}018.$

Find the radius of convergence, $R,$ of the series.

${\displaystyle \underset{n=1}{\overset{}{}}}\frac{n}{3^n}(x7{)}^n$

$R=$

Find the interval, I, of convergence of the series. $($Enter your answer using interval notation.$)$

$I=$

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