If $A \subseteq B$,then $A \cup B$ =

If ${N_a} = \{an : n \in N\}$,then the set ${N_6} \cap {N_8} = $

If $A, B, C$ are three sets,then $A \cap (B \cup C)$ is equal to

If $A, B$ and $C$ are non-empty sets,then $(A - B) \cup (B - A)$ equals:

If $A = \{ x : x \text{ is a natural number} \}$,$B = \{ x : x \text{ is an even natural number} \}$,$C = \{ x : x \text{ is an odd natural number} \}$,and $D = \{ x : x \text{ is a prime number} \}$,find $A \cap C$.

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