Ally is a famous fashion designer. I was talking with her at party last night.

이 문자 두개를 히ㅡㅂ치면

Ally is a famous designer with which whom I was talking at the party last night.

이렇게 되잖아? 여기 which앞에 왜 at이 아니라 with가 들어가는거야? 그리고 which 뒤에 whom 꼭 적어야해?