1. **State the problem:** We are given four points on a line: $(30,45)$, $(33,33)$, $(36,21)$, and $(39,9)$. We need to find the slope of the line passing through these points. 2. **Formula for slope:** The slope $m$ between two points $(x_1,y_1)$ and $(x_2,y_2)$ is given by: $$m=\frac{y_2 - y_1}{x_2 - x_1}$$ 3. **Calculate slope using first two points:** $$m=\frac{33 - 45}{33 - 30}=\frac{-12}{3}$$ 4. **Simplify the fraction:** $$m=\frac{\cancel{-12}}{\cancel{3}}= -4$$ 5. **Verify slope with other points:** Between $(33,33)$ and $(36,21)$: $$m=\frac{21 - 33}{36 - 33}=\frac{-12}{3} = -4$$ Between $(36,21)$ and $(39,9)$: $$m=\frac{9 - 21}{39 - 36}=\frac{-12}{3} = -4$$ 6. **Conclusion:** The slope of the line passing through all given points is $-4$.