Is 2, 6, 18, 54 arithmetic or geometric

Pls , the question is in the picture!

What describes horizontal cross section of the right rectangle 6m 8m 5m

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?