If you are preparing for a specific quiz, sites like Infourok provide sample tests for the Danilova curriculum that essentially function as an answer key. How to Download and Use Materials
Instead of searching for "Reshebnik," try searching for the Metodicheskoye Posobiye for your author; it provides the full context for every chapter.
Most schools use either Danilova or Sergeeva/Kashekova/Kritskaya . Ensure the guide matches your specific book.
Sites like Infourok and Calaméo host digital versions of the Sergeeva, Kashekova, & Kritskaya textbook and related materials where you can often find shared notes or test answers.
For the textbook, you can find official 8th-grade teacher manuals and 5-9 general guides on platforms like Rosuchebnik .
These are the most reliable "reshebniki" because they contain lesson plans, answers to textbook questions, and creative task ideas.
Large publishers like Prosveshcheniye offer electronic versions and supplementary materials that are often more complete than unofficial files.