あたしも賛成だから、三対一ね。というわけで、ハルカの反対意見は却下されました。

、。、。

I'm in favor too, so that's three to one. With that, Haruka's objection has been overruled.

Literal

I [also-も] in-favor [copula-だ]-[because-から], 3-versus-1-[confirming-ね]. That-being-the-case, Haruka [of-の] opposing-opinion [topic-は] was-rejected.

Informal group-decision scene with a mock-official finale. あたし is the feminine informal first-person pronoun (contrast with 私 watashi or 僕 boku). 三対一 uses the 対 counter-preposition for 'X-versus-Y' in scoring/voting/opposition. というわけで is a discourse connector 'so, with that.' 却下される is the passive of 却下する ('to dismiss/reject formally'), giving the sentence its intentionally over-formal decisive tone. Difficulty: 3