Two datasets, $A$ and $B$, have equal sizes $n_A = n_B$. Both datasets are symmetric and have the same standard deviation $\sigma_A = \sigma_B = 3$. However, their means are different, with $\bar{x}_A = 10$ and $\bar{x}_B = 16$. What is the standard deviation $\sigma_{\text{combined}}$ of the combined dataset?