Which is the better deal? question 2 options: 1 lb of apples for $2.50 3 lbs of apples for $4.25 5 lbs of apples for $7.20 10 lbs of apples for $15.00

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?