79. There are 12 balls, of which 4 are white, in an urn. Three players-A, B, C-successively draw from the urn, A first, then B, then C, then A, and so on. The winner is the first one to draw a white ball. Find the win probabilities for each player if

(a) each ball is replaced after it is drawn;

(b) the withdrawn balls are not replaced.