1. **State the problem:** Find the equation of line F in the form $y = mx + c$ given two points on the line. 2. **Identify points:** The line passes through points $(0, 80)$ and $(40, -90)$. 3. **Calculate the slope $m$:** Use the formula for slope: $$m = \frac{y_2 - y_1}{x_2 - x_1}$$ Substitute the points: $$m = \frac{-90 - 80}{40 - 0} = \frac{-170}{40} = -\frac{17}{4} = -4.25$$ 4. **Find the y-intercept $c$:** Since the line crosses the y-axis at $(0, 80)$, the y-intercept is: $$c = 80$$ 5. **Write the equation:** Substitute $m$ and $c$ into the slope-intercept form: $$y = -4.25x + 80$$ **Final answer:** $$y = -4.25x + 80$$