A food company is conducting research on customers' taste. In each round of a blind taste experiment four black teas and one herbal tea are presented to participants. Suppose that the participants randomly guess, independently in each round.

(a) If a participant picks the herbal tea in each of three rounds, a box of tea is won. What is the probability that a participant wins a box of tea?

(b) What is the expected number of participants until a second box of tea is won?