Discounts and free shipping function independently, and if you have a free shipping minimum set, the buyer will receive that as well if their purchase is above the minimum amount you’ve selected. This is based on the total value of the books before any other discount is applied. For example, if your minimum free shipping amount is $20 and a buyer buys $21 worth of books, but you have a discount that takes their total down to $18, they will still earn free shipping.