A bag contains 68 Chocolate numbered 1, 2, ..., 68. Before the game starts, Adam selects 9 different numbers from 1, 2, ..., 68 and writes them on a piece of paper. Then, he randomly selects 12 chocolate from the bag without replacement.

What is the probability that

a. All the numbers are selected?

b. Exactly 8 of his numbers are selected? Explain each step in solution, and what concept from Probability is used. Show all you work. Solution should be neat and clear.