英语I'm afraid so和I'm afraid not 分别的意思,什么时候用,举个例子~

I'm afraid so
恐怕是这样的
例句:
A:Did you lose your passport
B:I'm afraid so.If I have lost it,what can I do?
I'm afraid not
恐怕不行
例句:
A:Can we pay by LC?
B:I'm afraid not.We don't generally accept a letter of credit.