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If it is in Questions, then there is a small square down on the right of an answer that allows you to answer the person who asked that question. So for instance if you had posted in your post that the memory was down to 4%, and I as Alvadeer asked you in my answer to your post "How do you know.....etc", then that little "reply button" will show and it will say "reply to Alvadeer".
As Barb suggests, go to your original question. Look at your answers. Below each answer there is a space for you to reply to any who answered you, including me. You just have to press on "reply to......."
If, however, you want to reply here in discussions you will go to the top, and press on "comment here" and then on "post comment.
Go back to your original post (that's the link above) and post your answers.