1. **State the problem:** Find the slope of the line given by the equation $x = -3$. 2. **Understand the line:** The equation $x = -3$ represents a vertical line where all points have $x$-coordinate $-3$. 3. **Recall slope definition:** Slope $m$ is the change in $y$ divided by the change in $x$, i.e., $m = \frac{\Delta y}{\Delta x}$. 4. **Slope of vertical line:** For a vertical line, $\Delta x = 0$ because $x$ does not change. 5. **Division by zero:** Since $m = \frac{\Delta y}{0}$ is undefined, the slope of a vertical line is undefined. **Final answer:** The slope of the line $x = -3$ is **undefined**.