The problem above uses the concept of ratio and proportion. The ratio between the cost and amount of the organic milk should always be equal. The proportion between two cases is shown below,
($2.52 / 0.5 gallon) = (x / 4 gallons)
Solving for x gives x = 20.16. Therefore, 4 gallons of organic milk costs $20.16.
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Answer: if you times 12x2.75 I got 33 some she can spend $33.00 and not go over.