Where does "some" comes from?
Other exercises indicate that "some potatoes" would be Genitive картошки. and that the correct translation here is "the potatoes". In particular, there is:
Купи картошки и свари её.
where genitive is used to say "Buy some potatoes"
A moderator really needs to address this issue.
Potato in Russian is uncountable, as I understand, like milk or bread. You wouldn't say bake a bread or bake breads, or pour milks, pour a milk, you would say some in front of them. It's not like eggs or beers, where you could say boil an egg, boil eggs, or pour a beer or pour beers.