Computer science nea

essentially, try to waffle about every little aspect of your project that you can. the more words you write (making sure it still makes sense), the more your teachers will commend you (in my experience). just make sure its all relevant.
in your case, justifying the features of a problem i'd imagine would be to explain the problem and your solution in more detail, focusing on providing reasons as to why each aspect of it makes it a plausible problem in need of solving. just a reminder that your 'solution' will just be the thing you make, so the problem could be a gap in the market, or lack of database structure for a local shop, etc. so, try your best to explain as much about the problem as you can, and then try and go into a lot of detail about your planned project and how your idea(s) would help to resolve this problem.
try to research lots about it as well - this is a good way to start writing references to sources in your document (which makes you look smarter and is recommended to get higher marks), and also to increase word count by extracting pre-written and researched information from different sources.
for example, for my project i made a basic ecosystem simulation game/program using unity, so in my analysis section i researched and explained in detail a specific pathfinding algorithm, using websites and youtube to help me to understand it enough to write about it and make diagrams to further explain it. i also researched about procedural generation and talked a bit about that, too. basically just research individual things that you would need to know about or know how to do, and talk about them. building this knowledge also helps with actually creating the project later.
also, find and research different products that are similar to your problem and proposed solution, and talk about these in relation to your ideas and how they compare, etc. (in my case i looked at some ecosystem simulation games that are already out and have different features).
basically just talk about anything and everything related to your project lol. 'analysis' = overanalyse everything you can to sound clever and as though you know a lot about your project and ideas.
one more tip, (assuming you're in year 12) i'd recommend trying to keep on top of your nea work as you go through it, maybe even working a little ahead. getting it finished earlier not only feels great but helps you to focus more on revision as you get closer to more mocks and exams. it also gives your teachers more time to give you feedback. if your tutor is unhelpful the rest of the time, keep asking questions online and finding resources that can guide you through your nea. it does suck having to self teach stuff but itd be so worth it - its a nice feeling knowing that a good chunk of the marks i need have already been obtained, it makes the computer science exams a little less stressful.
good luck!!