1. **State the problem:** We need to find a linear equation that models the relationship between time $x$ (in hours) and battery charge $y$ (percentage) based on the given data. 2. **Identify the formula:** A linear equation has the form $$y = mx + b$$ where $m$ is the slope and $b$ is the y-intercept. 3. **Calculate the slope $m$:** The slope is the rate of change of battery charge with respect to time. Using points $(0,90)$ and $(1,70)$: $$m = \frac{70 - 90}{1 - 0} = \frac{-20}{1} = -20$$ 4. **Find the y-intercept $b$:** The y-intercept is the battery charge when $x=0$. From the table, when $x=0$, $y=90$, so: $$b = 90$$ 5. **Write the linear equation:** $$y = -20x + 90$$ 6. **Interpretation:** This means the battery loses 20% charge every hour. 7. **Check with another point:** At $x=3$, $$y = -20(3) + 90 = -60 + 90 = 30$$ which matches the table. **Final answer:** $$y = -20x + 90$$