Final answer:
The number of different permutations of the set {a, b, c, d, e, f} is 720.
Step-by-step explanation:
The number of different permutations of the set {a, b, c, d, e, f} can be found using the concept of factorial. In this case, we have 6 elements, so the number of permutations is 6 factorial, denoted as 6!. This can be calculated as 6 x 5 x 4 x 3 x 2 x 1 = 720. Therefore, the correct answer is a) 720.