Summary statistics for returns on two stocks $x$ and $Y$ are listed below.

$\backslash$table$[[,$Mean,Variance$],[$Stock $x,2\mathrm{.}71\%,0\mathrm{.}003000],[$Stock $Y,3\mathrm{.}16\%,0\mathrm{.}005000]]$

The covariance of returns on stocks $x$ and $Y$ is $0\mathrm{.}003900.$ Consider a portfolio of $70\%$ stock $x$ and $30\%$ stock $Y.$

What is the standard deviation of portfolio returns?

Please specify your answer in decimal terms and round your answer to the nearest thousandth $($e$.$g$.,$ enter $12\mathrm{.}3$ percent as $0\mathrm{.}123$

Note that the correct answer will be evaluated based on the full$-$precision result you would obtain using Excel.