the perimeter, p, of an equilateral triangle varies directly as the length of a side. if the perimeter is 153 cm when the side length is 51 cm, what would be the perimeter if the side length is 81 cm

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?