Stu is buying a $35 tool. the store reduces the price by 5% and then applies an $8 off coupon. how much will stu pay for the tool?

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?