Write down all the subsets of the following set: $\{a\}$

List all the subsets of the set $\{-1, 0, 1\}$.

If $P, Q$ and $R$ are subsets of $A$,then $R \times (P \cup Q) = $

If $D_{30}$ is the set of all divisors of $30$,$x, y \in D_{30}$,we define $x+y=\operatorname{LCM}(x, y)$,$x \cdot y=\operatorname{GCD}(x, y)$,$x^{\prime}=\frac{30}{x}$ and $f(x, y, z)=(x+y) \cdot (y^{\prime}+z)$,then $f(2, 5, 15)$ is equal to

Examine whether the following statement is true or false:
$\{a\} \in \{a, b, c\}$

If $A = \{x \in \mathbb{R} : x^2 + 5|x| + 6 = 0\}$,then $n(A) = $