How a Decision Tree Chooses a Split

A node of a classification tree holds 10 samples: 6 positive and 4 negative. A candidate split sends 6 samples left (5 positive, 1 negative) and 4 right (1 positive, 3 negative). Using Gini impurity $G=1-\sum_c p_c^2$, what is the impurity decrease (parent Gini minus the sample-weighted average of the children's Gini)? Give an exact fraction or decimal.