Provide an Appropriate Response $99 \%$ Confidence Interval for the Variance $\sigma ^ { 2 }$

Provide an appropriate response.
-The July utility bills (in dollars) of 20 randomly selected homeowners in one city are listed below. Construct a $99 \%$ confidence interval for the variance, $\sigma ^ { 2 }$ . Assume the population is normally distributed.
$\begin{array} { l l l l l l l l l l } 70 & 72 & 71 & 70 & 69 & 73 & 69 & 68 & 70 & 71 \end{array}$
$\begin{array} { l l l l l l l l l l } 67 & 71 & 70 & 74 & 69 & 68 & 71 & 71 & 71 & 72 \end{array}$