You can find the solutions for the 5th-grade mathematics workbook by T.M. Erina (designed for Vilenkin's textbook) through several online resources:
ГДЗ Рабочая тетрадь по математике 5 класс Ерина Т.М. You can find the solutions for the 5th-grade
Community pages often share these files for educational use. For instance, PDF versions of both parts are available in this VK educational community post . You can find the solutions for the 5th-grade