1. **State the problem:** Find the distance between points $R(-10, -3)$ and $S(-10, -8)$. 2. **Formula used:** The distance between two points $(x_1, y_1)$ and $(x_2, y_2)$ is given by $$d = \sqrt{(x_2 - x_1)^2 + (y_2 - y_1)^2}.$$ 3. **Apply the formula:** Here, $x_1 = -10$, $y_1 = -3$, $x_2 = -10$, and $y_2 = -8$. Substitute these values: $$d = \sqrt{(-10 - (-10))^2 + (-8 - (-3))^2} = \sqrt{0^2 + (-5)^2} = \sqrt{25}.$$ 4. **Simplify:** $$d = 5.$$ 5. **Interpretation:** Since the $x$-coordinates are the same, the points lie on a vertical line, so the distance is simply the absolute difference of the $y$-coordinates, which is $5$ units.