1. The problem is to find the value of $x$ when $y = -2.18$ for the function $y = -2.18$. 2. Since the function is a constant function $y = -2.18$, it means that for every value of $x$, $y$ is always $-2.18$. 3. Therefore, when $y = -2.18$, $x$ can be any real number. 4. This is because the graph of $y = -2.18$ is a horizontal line crossing the $y$-axis at $-2.18$. Final answer: $x \in \mathbb{R}$ (all real numbers).