Standard Deviation of Difference in Proportions

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, $\sigma_{\hat{p}_1 - \hat{p}_2}$?