How Many??

[gimpy]

Im trying to figure this question out from an old Final exam.

(a) In how many numbers with seven distinct digits do only the digits 1 to 9 inclusive appear (i.e. digit 0 is exluded)?

This one i got P(9,7) because there are 9 numbers and 7 ordered places to place 7 of the 9.

(b) How many of the numbers in (a) contain a 3 and a 6?

For this question i got C(7,5)*P(7,7). Don't know if this is correct....

(c) How many of the numbers in (a) contain neither a 3 nor a 6?

This one it's either
P(8,7) + P(8,7) - P(7,7)
or simply
P(7,7)

Im pretty sure i got (a) but for (b) and (c) i need some help. Am i close?

Thanks