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 homeowrk), 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](https://stats.stackexchange.com/tags/self-study/info); you can peruse out meta.CV threads regarding the policies by clicking on the [tag:homework] tag; you can see examples of how I've dealt with such questions [here](https://stats.stackexchange.com/q/190535/7290) and [here](https://stats.stackexchange.com/q/58718/7290).