Variance of first $2n$ natural numbers is

The frequency distribution is given below:
$\begin{array}{|l|l|l|l|l|l|l|} \hline X & 2 & 3 & 4 & 5 & 6 & 7 \\ f & 4 & 9 & 16 & 14 & 11 & 6 \\ \hline \end{array}$
Find the standard deviation.

The mean of a distribution is $4$. If its coefficient of variation is $58\%$,what is the standard deviation of the distribution?

Let $x_{i} (1 \leq i \leq 10)$ be ten observations of a random variable $X$. If $\sum_{i=1}^{10} (x_{i} - p) = 3$ and $\sum_{i=1}^{10} (x_{i} - p)^{2} = 9$,where $0 \neq p \in R$,then the standard deviation of these observations is:

If the variance of observations $x_1, x_2, \dots, x_n$ is $\sigma^2$,then the variance of $ax_1, ax_2, \dots, ax_n$,where $a \neq 0$,is

The standard deviation of the numbers $22, 26, 28, 20, 24, 30$ is