This is the 10th most frequent Korean word.
전
The Korean word "전" can mean "before," "former," or refer to "jeon," a savory pancake-like dish, depending on context.
In this sentence, '전' is used as a contraction of '저는', which is the subject pronoun 'I' in nominative case in Korean.
전 그 일을 모르고 있었습니다.
I did not know about that matter.
Here, '전' means 'before' and is used to indicate a time preceding the 'exam'.
시험 전에 공부를 많이 해야 해요.
You need to study a lot before the exam.
In this one, '전에' includes '전' as part of the word indicating 'before' or 'prior to' a certain event.