Find the sum of the interior angles of a nonagon

Which value is not a solution of 8x^3 – 1 = 0

25 ! i need asap! ! ill mark brainliest!

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?