If $aN = \{ ax:x \in N\} ,$ then the set $3N \cap 7N$ is .....$N$

Which of the following pairs of sets are disjoint 

$\{ x:x$ is an even integer $\} $ and $\{ x:x$ is an odd integer $\} $

If $X = \{ {4^n} - 3n - 1:n \in N\} $ and $Y = \{ 9(n - 1):n \in N\} ,$ then $X \cup Y$ = . . . . .

Let $A=\{1,2,3,4,5,6\}, B=\{2,4,6,8\} .$ Find $A-B$ and $B-A$

Show that if $A \subset B,$ then $(C-B) \subset( C-A)$

Let $A$ and $B$ be sets. If $A \cap X=B \cap X=\phi$ and $A \cup X=B \cup X$ for some set $X ,$ show that $A = B$

( Hints $A = A \cap (A \cup X),B = B \cap (B \cup X)$ and use Distributive law )