What are all the elements that are in A or B? Well, we can just literally put all the elements in A. 11, 4, 12, 7. And then put the things in B that aren't already in A. So let's see, 13, we already put the 4 and the 12, a 10, and a 3. And I could write this in any order I want. We don't care about order if we're thinking about a set.