This is the 17265th most frequent Russian word.
сумку
"Сумку" is the accusative form of "сумка," meaning "bag" in English.
Here, 'сумку' is in the accusative case, denoting the direct object of the verb 'купил' (bought).
Я купил новую сумку.
I bought a new bag.
'Сумку' is in the accusative case, governed by the preposition 'в' with the verb 'положил' to indicate direction (into the bag).
Я положил в сумку книгу.
I put the book into the bag.
In this sentence, the nominative form 'сумка' is used as the subject of the verb 'стоит' (costs).