A random sample $\displaystyle x_{1}...x_{n}$, n=200, is taken from a distribution with mean $\displaystyle \mu$ and variance $\displaystyle \sigma^2$, both are unknown. Find unbiased estimators of the mean and variance, given

$\displaystyle \sum_{i=1}^{200}x_{i}=308$ and $\displaystyle \sum_{i=1}^{200}x_{i}^2=3784$

I don't even know where to start. Can anyone give me any help please?