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(b) the withdrawn balls are not replaced.