1. **State the problem:** Find the vertical distance between points $A(-1, 1.5)$ and $B(-1, -1.5)$. 2. **Formula:** The vertical distance between two points with the same $x$-coordinate is the absolute difference of their $y$-coordinates: $$\text{Vertical distance} = |y_2 - y_1|$$ 3. **Apply the formula:** Here, $y_1 = 1.5$ and $y_2 = -1.5$. $$|y_2 - y_1| = |-1.5 - 1.5|$$ 4. **Calculate:** $$|-3| = 3$$ 5. **Conclusion:** The vertical distance between points $A$ and $B$ is $3$ units.