In a formal outline, numbers and letters are used to arrange topics and subtopics. It will increase credibility of the paper and makes good impression about its writer. If you've time and alternative, present it to your teacher to revise.
It's clear from the highlighting and underlining that the prof wants an argumentative paper that is well-organized and thoughtful. Now that you have that discovered, let's transfer on to the subsequent step: Crafting a reminder that you could revisit