(8 marks) Suppose that all licence plates consist of three symbols chosen from the 26 letters of the alphabet followed by three or four of the digits 0-9. (a) How many licence plates are possible if repetition of symbols is allowed? (b) How many licence plates do not contain any repeated symbol? (c) How many licence plates have at least one repeated symbol? (d) What is the probability that a licence plate chosen at random has a repeated symbol