I know how to calculate covariance and correlation, just not in this question... I'll explain why after I write out.

Suppose that $\displaystyle X_1$, $\displaystyle X_2$, $\displaystyle X_3$, $\displaystyle X_4$, $\displaystyle X_5$ are independent random variables with variance $\displaystyle \sigma^2$. Determine the covariance of $\displaystyle X_1+3X_2+2X_3$ and $\displaystyle 2X_1-X_2+3X_4+X_5$? Determine the correlation between these two variables.

Now, as far as I'm aware, you need to know the means to calculate the covariance am I being an idiot and missing something completely obvious?