Determine whether each of these sets is countable or uncountable.

Ive been having issues with a question on my assignment:

Determine whether each of these sets is countable or uncountable. For those that are countably infinite,

exhibit a one-to-one correspondence between the set of positive integers and that set.

1. integers not divisible by 3
2. integers divisible by 5 but not by 7
3. the real numbers with decimal representations consisting of all 1s
4. the real numbers with decimal representations of all 1s or 9s