A fair die is rolled. a. If the die is rolled 8 times, what is the probability that the die comes up 6 exactly twice? b. If the die is rolled until the first 6 comes up, find the probability that the first 6 occurs on the 4th roll. c. If the die is rolled until the third 6 comes up, find the probability that the third 6 occurs on the 5th roll.