Since you are looking to download or view these for free, several reputable Russian educational platforms host them. You can usually find the solutions for both of the textbook:
Have the student complete the exercise first, then use the GDZ to find and correct their own mistakes. Since you are looking to download or view
Tricky spelling rules that usually appear in 4th grade in other programs. Best Practices for Using GDZ Best Practices for Using GDZ Polyakova’s exercises often
Polyakova’s exercises often require a specific reasoning. If the GDZ provides an explanation for a comma or a vowel choice, make sure the student reads it. Why Polyakova’s 3rd Grade is Unique This site
Known for having very clean, typed-out explanations rather than just handwritten notes, making it easier to read. Why Polyakova’s 3rd Grade is Unique
This site often provides a "flipbook" view of the textbook with answers filled in, which is very convenient for quick checking.