I'm looking for recommendations on undergrad math books, in the topics of calculus, elementary set theory, linear algebra and combinatorics.
I'm not sure when / in which format I should be asking this question.
You can ask that on the main site. But I suggest
First you search the site for similar questions. The topics that you are interested in are very standard and you can find a lot of these questions under the tag "book-recommendation" (This is what I found under the tags [book-recommendation] and [linear-algebra], ordered by votes).
If you have some special criterion and all of those posts do not address that, you may ask a new question. But make sure to make your post distinct from the old ones, convince everyone that a new post is necessary. If not the post will be quickly closed as duplicates.