Whether you use calculus or statistics will depend on what career you end up in. Statistics are used in many industries to prove cause and effect in order to improve processes. They are very important in the pharmaceutical, manufacturing, and other businesses as well, but you could be in a position in those industries where you have no need to use statistics.
Same for calculus. It was required as a prerequisite in one MBA school, but not in another. So in some business environments, it may be useful. In others, you'll never need to use it.
When I was considering one MBA school that did require calculus as a prerequisite, I took a proficiency exam to satisfy the requirement. I had never had calculus before, so I asked for an outline of the knowledge required and studied the first 6 chapters of the book The Complete Idiot's Guide to Calculus. It made calculus fairly easy to understand (for me, anyway), and I passed the proficiency exam for calculus. It didn't make me an expert in the subject, but if you want a good starting point as a refresher for calculus, I can recommend this book.
For statistics, I can't recommend any book on my own experience. I learned what I needed during an intensive 160 hour training course in Six Sigma techniques. But I would bet that this book would also be a good starting point for you as a refresher: The Complete Idiot's Guide to Statistics.
Both are available on Amazon.com. You can get both as used books there for less than $18 including shipping.