I've actually done a three-page article on the gender pay gap so can give you some pointers! I haven't done any formal economic reports, only essays, but my advice for any academic piece of writing comprises of a few steps that are easily missed.
1. Grammar, spelling and structure are important - make sure you get someone else to read it and see if it makes sense.
2. Write in plain English, don't go too formal on the tone - just be clear and concise.
3. Think about your argument and break the question down to think about the topics/points you want to cover.
4. Have a detailed plan so you don't miss anything out.
5. Use at least one example/statistic to back up your argument, and make sure you reference the source.
6. Don't leave writing it to the last minute - take your time and make sure you edit, proofread and polish it.
7. Make sure you stay focussed on the question and don't deviate too much from it.
Also, regarding your questions, I would say that a) for a structure, a clear introduction, three detailed points with counter arguments/evaluation and a thorough conclusion is a good bet, and b) as for content, if you haven't started economics they can't expect something really technical; try and do some research and just try to understand what the gender pay gap is and what some potential solutions are - there are lots of articles and reports out there giving many suggestions.
Good luck!