I know this has been answered, but i still want to explain it, if you wanted help
2n <span>≥ 15
work:
extract the elements of the problem. </span><span> Twice a number (we will use 2n because we don't know the number) at least 15 (</span>≥ 15 make sure you have the line underneath the equality symbol! "at least 15" means it ca also be 15!)