document.write( "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? \n" ); document.write( "
Algebra.Com's Answer #390812 by dragonwalker(73)\"\" \"About 
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Let us call the cost of regular 'g' so the cost of premium is 'g+0.21'
\n" ); document.write( "Multiply the number of gallons by its cost per gallon for each type and add together which will equal $56.64 so:\r
\n" ); document.write( "\n" ); document.write( "6g + 9(g+0.21)=56.64\r
\n" ); document.write( "\n" ); document.write( "solve for g:\r
\n" ); document.write( "\n" ); document.write( "6g + 9g + 1.89 = 56.64
\n" ); document.write( "15g = 56.64-1.89 (when moving a number from one side to the other side of an equation change the sign)\r
\n" ); document.write( "\n" ); document.write( "15g = 54.75\r
\n" ); document.write( "\n" ); document.write( "divide both sides by 15 to find g:\r
\n" ); document.write( "\n" ); document.write( "15g/15 = 54.75/15\r
\n" ); document.write( "\n" ); document.write( "g = 3.65\r
\n" ); document.write( "\n" ); document.write( "So the cost of regular is $3.65 and therefore the cost of premium is g+0.21 = $3.86 \r
\n" ); document.write( "\n" ); document.write( "To check:
\n" ); document.write( "6(3.65) + 9(3.86) = 56.64 !!!
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