How much of an item or text can I use for my class?
Copyright law does not provide a specific set of rules to follow. Instead, it is intentionally left vague to allow "fair use". With that said, less is always better under fair use recommendations. Also please remember, the "heart" or "main part" of a work, no matter how small, is too much. The exception is that an entire image, news article, or graph may be needed for instruction; you must give credit, including a copyright notice, with any use of copyrighted material.