2. [4 marks] (a) How many different strings of 4 letters can be formed from the letters of the word sandworm, without repetition? (b) If a 4-letter string from the letters in sandworm is chosen at random, what is the probability it is snow? (c) How many different 4-element subsets of the set {s, a, n, d, w, o, r, m} are there? (d) If a 4-element subset of {s, a, n, d, w, o, r, m} is chosen at random, what is the probability it is {s, n, o, w}?