Answer:
water = 100 gallons
antifreeze = 30 gallons
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Step-by-step explanation
x = amount of water
y = amount of premium antifreeze solution
Each amount is in gallons
This premium solution contains 65% pure antifreeze, which means 0.65y represents the amount of pure antifreeze in gallons.
The idea is to divide 0.65y over the total 130 and we'll get the proportion of antifreeze in the final mix. We want this proportion to be 0.15 to represent a 15% solution.
0.65y/130 = 0.15
0.65y = 130*0.15
0.65y = 19.5
y = 19.5/0.65
y = 30
You'll need 30 gallons of the premium antifreeze solution.
And,
x+y = 130
x+30 = 130
x = 130-30
x = 100
You'll also need 100 gallons of water.