I'm a professional auditor. I looked through the key guidance I use regularly and it doesn't include a definition of "material" - it's assumed professional knowledge. The GAO's Yellow Book (gao.gov/assets/700/693136.pdf) and AICPA standard on materiality (aicpa.org/Research/Standards/AuditAttest/DownloadableDocume‌​nts/…) contain numerous examples.

If these solutions are readable by the OP's target audience, than it's hard to imagine a better answer.

This looks like a word usage question that can be answered easily enough. The edits also illustrate the source of confusion. Seems like this can be re-opened.

Thanks, Brian. I've updated the post with the correct spelling.

That follows the same convention. There is no hyphen between the units and the object being measured. It isn't "3-year-old-house".