1. **State the problem:** Larissa's laptop battery started at 100% and after 3 hours it was at 79%. We need to find the average change in battery charge per hour. 2. **Calculate the total change in battery charge:** $$\text{Change} = 79\% - 100\% = -21\%$$ This means the battery charge decreased by 21% over 3 hours. 3. **Calculate the average change per hour:** $$\text{Average change per hour} = \frac{-21\%}{3 \text{ hours}} = -7\% \text{ per hour}$$ 4. **Interpretation:** The battery charge decreases by 7% each hour on average while Larissa is working on her design. **Final answer:** The average change in Larissa's battery charge each hour is $-7\%$ per hour.