x = cost of 5 gallons of regular

x + 0.18 = cost of 10 gallons of premium {premium is $0.18 more than regular per gallon}

5x + 10(x + 0.18) = 31.05 {number of gallons times price per gallon equals total price}

5x + 10x + 1.8 = 31.05 {used distributive property}

15x + 1.8 = 31.05 {combined like terms}

15x = 29.25 {subtracted 1.8 from each side}

x = 1.95 {divided each side by 15}

x + 0.18 = 2.13 {substituted 1.95, in for x, into x + 0.18}

**$1.95 is the price per gallon of 5 gallons of regular
**

$2.13 is the price per gallon of 10 gallons of premium*- Algebra House*
**
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