A large aggregator where you can search by author (e.g., Ershova, Popov) to find step-by-step solutions for paper-based assignments.

Often publishes independent workbooks specifically tied to the popular Vilenkin mathematics textbooks. Where to Find Solutions

, I can find the exact link or solution set for you.

To find the exact solution for your paper workbook, search for: The (e.g., 7 класс). The Subject (Algebra, Geometry, etc.). The Author's last name (found on the front cover).