1. Problem: Find the percent increase in oil price when it changed from ₱30.00 to ₱31.35 per liter. 2. Calculate the increase in price: $$\text{Increase} = 31.35 - 30 = 1.35$$ 3. Use the formula for percent increase: $$\text{Percent Increase} = \frac{\text{Increase}}{\text{Original Price}} \times 100\% = \frac{1.35}{30} \times 100\%$$ 4. Compute the percentage: $$= 0.045 \times 100\% = 4.5\%$$ 5. Conclusion: The oil price increased by 4.5%.