If a varies directly as m and n^2 and inversely as y^3, and a = 9 when m = 16, n=9, and y=3, find a if m=3, n=4, and y = 5.

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?