There's no particular need to use the commenting feature. You can use comments or the answer field. The issue is that if the post is a homework-type question (people will sometimes say it's not homeowrkhomework), then our policy is to provide hints to help the OP figure it out for themselves. Once they've figured it out, you can post a final, complete answer. This only applies to homework-type questions, though. Our homework policies are listed here; you can peruse out meta.CV threads regarding the policies by clicking on the homework tag; you can see examples of how I've dealt with such questions here and here.