A sample of size 400 has a (sum)x = 30,430 and (sum)xsquared = 3,261,1000.

construct a 95% confidence interval for the approriate mean (mew).

I got the t-score to be 1.966 and the x avaerage to be 76.075 but when trying to do the confidence interval I don't know what to put in for s becuase i don't know how to find s (part of the studentized version) s is equal to standard deviation. does anyone know how to find this?