Solve the inequality $-6x \leq 18$ for the following cases:
$(1)$ $x \in N$
$(2)$ $x \in Z$
$(3)$ $x \in R$

(N/A) Given inequality: $-6x \leq 18$
Divide both sides by $-6$. Remember that dividing by a negative number reverses the inequality sign:
$x \geq \frac{18}{-6}$
$x \geq -3$
$(1)$ If $x \in N$ (Natural numbers: $\{1, 2, 3, \ldots\}$),then $x \in \{1, 2, 3, \ldots\}$.
$(2)$ If $x \in Z$ (Integers: $\{\ldots, -2, -1, 0, 1, 2, \ldots\}$),then $x \in \{-3, -2, -1, 0, 1, 2, \ldots\}$.
$(3)$ If $x \in R$ (Real numbers),then $x \in [-3, \infty)$.