Sorted Union. I need help

Hello, I am working on a sorted union algorithm problem. And I’m not getting it. I’ve tried for loops and I’ve tried map. Plus, I’m not sure how to use the reduce method on this.

Have you tried writing out an algorithm to see if your written steps can be followed all the way through to arrive a a correct answer for a given test case? Please provide your algorithm to us and we can at least make sure you are on the correct path before you even try to write any code.