A radio station gives a pair of concert tickets to the sixth caller who knows the birthday of the performer. For each person who calls, the probability is 0.75 of knowing the performer's birthday. All calls are independent.
(a) What is the PMF of L, the number of calls necessary to find the winner?
(b) What is the probability of finding the winner on the tenth call?
(c) What is the probability that the station will need nine or more calls to find a winner?