Two urns each contain ten balls. Urn A contains three red balls and seven blue balls. Urn B contains six red balls and four blue balls. One of the urns is selected at random, and then two balls are selected at random without replacement from the selected urn.
(a) What is the probability that both balls selected are red?
(b) Given that both ball selected are red, what is the probability that the selected urn was urn A?