- I will meet you at the office, or,
- I will meet you in the office.
However, if you want to tell others whether you are at work or not then in the office should used, for examples,
- Yes, I have to work on Monday, I will be in the office.
- No, I don't have to work on Monday, I will not be in the office.
Further, the use of "in" or "at" makes a difference in the following situations:
- I teach English in unversity.
- I teach English at the Hong Kong Unversity.
"In" should be used if the type of school in general is referred to. In the first example "in university" is used because you are telling others that you are teaching university level, not middle school, not primary schoo. "At" should be used if one specific school is referred to, In the second example "at" is used because you want to tell people that your are not only teaching university level but also at HK university and not any other universities.
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