For 10 observations x_1, x_2, …, x_10, if Σ_i=1^10(x_i+2)^2=180 and Σ_i=1^10(x_i-1)^2=90, then their standard deviation is:

For $\displaystyle 10$ observations $\displaystyle x_1, x_2, \ldots, x_{10}$, if $\displaystyle \sum_{i=1}^{10}\left(x_i+2\right)^2=180$ and $\displaystyle \sum_{i=1}^{10}\left(x_i-1\right)^2=90$, then their standard deviation is: