18.3%.
To calculate the percentage increase in gas price:
1. Find the difference in price: $1.55 - $1.31 = $0.24
2. Divide the difference by the original price: $0.24 / $1.31 ≈ 0.183
3. Multiply by 100 to get the percentage: 0.183 * 100 ≈ 18.3%
So, the gas price increased by approximately 18.3%.
