The appositive usually agrees with the noun it describes. In this example, both "реку" and "Волгу" are in the Accusative case (винительный падеж) because they follow the preposition "в." Punctuation with Names:
If a common noun (like река ) comes a proper name ( Волга ), you generally do not use a hyphen. The appositive usually agrees with the noun it describes
Provides a clear view of the corrected text and the grammatical reasoning behind the punctuation. The appositive usually agrees with the noun it describes
A standard resource for checking Russian language homework for the Trostentsova 8th-grade curriculum. The appositive usually agrees with the noun it describes
If you need to verify other sentences from this specific exercise, you can find step-by-step breakdowns on educational platforms:
Bridge TEFL 
Expert Series Webinars 
BridgeUniverse Blog 
TEFL Jobs 
Language Training 
About Bridge