First remark about the word garage , in arabic, the equivalent is not garage, we could say دكان (doukkane)
Second one, the sound is not correct, if we suppose that garage is the right word, then the correct sentence sould be ( garajoki momtaz ya samia, not garajiki momtaz ' )
It is actually the grammatical case difference, but in this course they use it for gender because they are mixing Arabic with some dialect. In Arabic, the gender marking is after the kaaf i.e. karajuka and karajuki.