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Ineed on this question me get the answer

Answer asap and if you do you will get brainliest. catherine buys a gallon of ice cream from the store. after taking it home, she eats a fifth of a gallon of ice cream. her sister eats some of the ice cream as well. if two-thirds of the original amount of ice cream is left, then what fraction of a gallon of ice cream did her sister eat?

1- how are translations represented as a function? . . 2- what is the relationship between a translation and a rigid motion? answer my grade depends on it! you so much