# SOLUTION: Lydia decides to mix grades of gasoline in her truck. She puts in 6 gallons of regular and 9 gallons of premium for a total cost of \$56.64. If premium gasoline costs \$0.21 more pe

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 Question 621570: Lydia decides to mix grades of gasoline in her truck. She puts in 6 gallons of regular and 9 gallons of premium for a total cost of \$56.64. If premium gasoline costs \$0.21 more per gallon than regular, what was the price of each grade of gasoline?Answer by dragonwalker(72)   (Show Source): You can put this solution on YOUR website!Let us call the cost of regular 'g' so the cost of premium is 'g+0.21' Multiply the number of gallons by its cost per gallon for each type and add together which will equal \$56.64 so: 6g + 9(g+0.21)=56.64 solve for g: 6g + 9g + 1.89 = 56.64 15g = 56.64-1.89 (when moving a number from one side to the other side of an equation change the sign) 15g = 54.75 divide both sides by 15 to find g: 15g/15 = 54.75/15 g = 3.65 So the cost of regular is \$3.65 and therefore the cost of premium is g+0.21 = \$3.86 To check: 6(3.65) + 9(3.86) = 56.64 !!!