Drag each object to show weather cost is proportional to area in the situation represented. (Right answer gets brainliest)

Which equation represents a proportional relationship that has a constant of proportionality equal to 1/5

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Last month, a 770 g box of cereal was sold at a grocery store for $3.10. however, this month, the cereal manufacturer launched the same cereal in a 640 g box, which is being sold at $2.50. what is the percent change in the unit price?