What is 1+1 and then -1 but then +1 and then minus 1 but then add 2 but then subtract 1 and then add 100 and divide by 1 and then subtract 100 and then multiply by 1 and then you add 0?

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?