If you are going to do PhD economics after graduation, you might want to read the beginning chapters of Hayashi. Though it is a graduate-level book, it is readable for undergraduates with good understanding of the material in a typical prob-stat sequence. Alternatively, Greene might also be a good choice.
For linear algebra, I once read Leon's book several years ago and felt that it was a good one. You may also want to try Friedberg's classic text on linear algebra. That one contains a bit more "theory" than Leon's and is very rigorous. I heard that Linear Algebra Done Right by Axler is also very good, but I have not read that.