11) Box 1 contains 4 white balls and 2 black balls. Box 2 contains 2 white balls and 2 black balls. Two balls are to be selected from box 1 and placed into box 2. From box 2, two balls are to be selected at random without replacement. If the two sample balls from box 2 were white, what is the probability that the transferred balls from box 1 were black. (10 points)