You have 9 options for the first position (all except zero); 9 options for the second position (any digit except the digit used for the first position; 8 options for the third position; 7 options for the fourth position; 6 options for the fifth position; and 5 options for the sixth position. Multiply everything together.
24
256
Without repeating digits (not digets!) and without leading 0s, 600 of them.
60
It is a repeating decimal.
256
24
18, if leading 0s are disallowed.
Without repeating digits (not digets!) and without leading 0s, 600 of them.
98765
60
468, 486, 648, 684, 846, 864.
86420
It is a repeating decimal.
-58264
4 x 3 x 2 ie 24
5040