Which of the following is not a perfect square trinomial?

144 + 12y + y2

100 + 20y + y2

64 – 16y + y2

25 + 10y + y2

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?