An ordinary die is tossed once. If a 1 appears, a ball is drawn from Urn 1. If a 2, 3 or 4 appears, a ball is drawn from Urn 2; otherwise, a ball is drawn from Urn 3. Urn 1 contains 5 white, 3 green and 2 red balls. Urn 2 contains 1 white, 6 green and 3 red balls. Urn 3 contains 3 white, 1 green and 6 red balls.

a.What is the probability that a red ball is drawn?

b.What is the probability that Urn 2 is selected if a red ball is drawn?