Hi
@flower1, I think you've covered the bulk of what could potentially be asked in a written exercise, unless the firm wants to throw in a little curveball and provide another format, but generally what it is assessing will be the same.
We don't have any materials on the structure (from what I can gather at least) but I would say that it is probably wise not to focus too much on the structure, as opposed to the audience/technique in writing. Of course, structure helps, but remember this is more so to make this concise and easy to digest - so ask yourself, if you were the intended audience (in that position) how would you like the information to be presented to you e.g. if I was a client, I would want the overall answer (whether you call that an exec summary or not), then I'd want you to break down the main points, lastly ending on any next steps you may need from me. Understanding your audience will guide your structure.
Everyone's structure will be a little different, so firms will not really have a set template as to how you should have broken down the information, just that you've attempted to do so efficiently.