I'm not trying to teach you Russian. I'm giving an example in a language you're familiar with.

I can give an example from Germanic languages.

Old English: tōdæġ (modern English "today")

Swedish: idag "today"

Dutch: vandaag "today"

Same root ("day"), same meaning ("today"), but different languages chose different prepositions/prefixes (to-, van-, i-).

Just like with s- vs. za- in Russian/Serbian.