This represents the distributive property. The distributive property means you can "distribute" the 1/2 to what's inside the parentheses - that is, to the 6 (1/2 times 6 = 3) and to the 4 (1/2 times 4 = 2). Put another way, it means you can multiply each addend separately, and then add the products together to get the right answer..
