Very stupid question, but really need

$\displaystyle \Sigma$$\displaystyle x$=24095,7 ($\displaystyle \Sigma$x$\displaystyle =n*m=25*963,828=24095,7$

$\displaystyle \Sigma$$\displaystyle x^2$=24991420,5

how to get $\displaystyle \Sigma$$\displaystyle x^2$ ???