For any two sets $A$ and $B$, $A-(A-B)$ equals

If $A = \{x \mid x \in N, x \text{ is a prime number less than } 12\}$ and $B = \{x \mid x \in N, x \text{ is a factor of } 10\},$ then $A \cap B = \dots$

If $A = \{3, 6, 9, 12, 15, 18, 21\}$,$B = \{4, 8, 12, 16, 20\}$,$C = \{2, 4, 6, 8, 10, 12, 14, 16\}$,and $D = \{5, 10, 15, 20\}$,find $C - A$.

In a school,there are three types of games to be played. Some students play two types of games,but none play all three games. Which Venn diagram$(s)$ can justify the above statement?

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

Consider the following relations:
$(1) \, A - B = A - (A \cap B)$
$(2) \, A = (A \cap B) \cup (A - B)$
$(3) \, A - (B \cup C) = (A - B) \cup (A - C)$
Which of these is/are correct?