9. Word of mouth advertising can be an effective form of marketing, or it can be very harmful. Consider a new restaurant that serves 27 customers on its opening night. a. Of the 27 customers, 25 found the experience enjoyable and each told 3 friends over the next month. This group each told 3 friends over the next month, and so on, for 6 months. Assuming that no one heard twice, how many people have had a positive experience or heard positive reviews of the restaurant? b. Suppose the 2 unhappy customers each told 6 friends over the next month about the experience. This group then each told 6 friends, and so on, for 6 months. Assuming that no one heard a review twice, how many people have had a negative experience or heard a negative review?