Answer
a) 216
b) 120
Work Step by Step
a) There are 6 possibilities for the first digit, 6 for the second, and 6 for the third. In total there are $6 \times 6 \times 6 = 216$ possibilities.
b) There are 6 possibilities for the first digit, 5 for the second, and 4 for the third. In total there are $6 \times 5 \times 4 = 120$ possibilities.
