Telephone numbers are preceded by a 3-digit area code (e.g. 514). In the following questions, any digit from {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} can be used unless otherwise stated. How many area codes are possible if:

1. the third digit must not be 7?
2. the digit 6 must not be used?
3. all three digits must be the same? e.g. 8-8-8
4. the first digit cannot be 0 or 1, the second digit cannot be 6 or 8, and the third digit must be 8?