The proportion of customers at a revamped restaurant who leave at least 100 calories on their plate is $$p_1 = 0.25$$. For an unrevamped restaurant, this proportion is $$p_2 = 0.19$$. If a random sample of $$n_1 = 110$$ customers is taken from the revamped restaurant and an independent random sample of $$n_2 = 120$$ customers is taken from the unrevamped restaurant, what is the standard deviation of the difference in sample proportions, $$\sigma_{\hat{p}_1 - \hat{p}_2}$$?