Saki doesn't understand why she was taken to play mahjong but that's where Saki and Nodoka met. Nodoka wins but questions Saki's playing style so she asks for another game.
Well if you already know each other,
that makes things easier.
باعتبارِكما على معرفة مُسبَقة
فهذا يُبسِّطُ المسألة
Si se conocen, me facilita las cosas.
Super, 
si vous vous connaissez déjà…
Beh, se vi conoscete già, è tutto più semplice.
Bem, se vocês já se conhecem, melhor ainda.