Like you, students often ask me impossible questions. What is the length of an article? How long should I research it? How long will it take me to write? How long should I spend on editing? If you look through publications, you will see similar topics but of hugely varying lengths. Some have photos, some don't. Some have drawings, some don't. Some are on the front page, and most aren't. Your questions simply don't have neat answers. I always reply with the inscrutable questions-in-reply:
How long is piece of string?
How thick is it?
What colour is it?
I tease you with the string because the honest answer is: an article is exactly as long as it needs to be, and not one word longer. But that is no use to a freelancer staring at a blank page, so let me give you something more practical to work with.
The length is not really your decision. It is the publication's. So before you write a line, go and count. Find three or four pieces in your target outlet that are similar to yours, a news item, a feature, a column, whatever you are aiming at, and count the words. That number, give or take, is your target. Editors think in terms of the space they have on the page, and a writer who delivers to that space, without being asked twice, is a writer they keep.
Then, when you write, fill that space with substance, not padding. A common beginner's mistake is to stretch a thin story to hit a word count. Never do it. The reader can feel the air in a padded piece. It is far better to file a tight 600 honest words than a flabby 900, and editors would rather cut your best work down than pump your thin work up.
So: match the house length, then make every word in it earn its keep. That is the real answer the piece of string was hiding.