Hey

I've just been stuck on this question for a while and can't seem to figure out how to do it. I would appreciate any help.

Problem:

Consider 3 urns. Urn A contains 2 white and 4 red balls, Urn B contains 8 white and 4 red balls, and Urn C contains 1 white and 3 red balls. If 1 ball is selected from each urn, what is the probability that the ball chosen from urn A was white given that exactly 2 white balls were selected.

Thanks!