1. **State the problem:** David can plant 300 flowers in the same time Sarah plants 240 flowers. David plants 10 more flowers per hour than Sarah. We want to find Sarah's planting rate $S$ (flowers per hour). 2. **Write the equation:** Given $\frac{300}{D} = \frac{240}{S}$ where $D$ and $S$ are David's and Sarah's rates respectively. 3. **Express David's rate in terms of Sarah's rate:** Since David plants 10 more flowers per hour, $D = S + 10$. 4. **Substitute $D$ into the equation:** $$\frac{300}{S + 10} = \frac{240}{S}$$ 5. **Cross multiply:** $$300 \times S = 240 \times (S + 10)$$ 6. **Expand the right side:** $$300S = 240S + 2400$$ 7. **Subtract $240S$ from both sides:** $$300S - 240S = 2400$$ $$\cancel{300S} - \cancel{240S} = 2400$$ 8. **Simplify:** $$60S = 2400$$ 9. **Divide both sides by 60:** $$\frac{60S}{\cancel{60}} = \frac{2400}{60}$$ $$S = 40$$ 10. **Answer:** Sarah can plant **40 flowers per hour**.