"Odpowiedziałam już na twoje pytanie."

Translation: I have answered your question already.

[AdamMlodoz]

In what cases do you use 'na' , 'dla', 'za' for the word 'for'? I can't figure out when to use these prepositions

[chb0lingo]

There are not always clear cases. And, translating directly from another language is hit and miss.

If you're really interested, there is a book: Polish grammar in a nutshell (za darmo)
http://www.skwierzyna.net/polishgrammar.pdf

[mihxal]

In this case it's always "odpowiadać na" when you answer a question and "odpowiadać za" when you are responsible for something. In Polish this verb is intransitive (nieprzejściowy), whereas in English it is transitive. Look at "składnia" (syntax): https://pl.wiktionary.org/wiki/odpowiada%C4%87

[Xelareip]

"I already answered to your question"?

[Jellei]

"to answer to" has a different meaning in English.

[Stewart288923]

Can i not use 'replied' instead of 'answered'?

[Walkinthedog]

Why does this need to hve the word have?

[alik1989]

In standard British English, "already" is an indicator for present perfect. But I guess there is no harm in accepting simple past as well.