Write down all the subsets of the following set: $\emptyset $

If $n(A) = 3$ and $n(B) = 6$ and $A \subseteq B$,then the number of elements in $A \cap B$ is:

Let $A = \{ \theta : \sin(\theta) = \tan(\theta) \}$ and $B = \{ \theta : \cos(\theta) = 1 \}$ be two sets. Then

In the following,state whether $A = B$ or not:
$A = \{ x: x \text{ is a multiple of } 10 \}$
$B = \{ 10, 15, 20, 25, 30, \ldots \}$

List all the elements of the following set:
$C = \{ x : x \text{ is an integer; } x^2 \le 4 \}$

Let $A$ and $B$ be two non-empty subsets of a set $X$ such that $A$ is not a subset of $B$. Then: