Paul is making brownies and the recipe calls for 5 and 1/2 cups of flour. he wants to do half of the recipe. how much flour is needed

There are three bags: a (contains 2 white and 4 red balls), b (8 white, 4 red) and c (1 white 3 red). you select one ball at random from each bag, observe that exactly two are white, but forget which ball came from which bag. what is the probability that you selected a white ball from bag a?