Hi, Each item/creation is subject to its' own license and you need to make sure that the license permits you to use whatever you purchased for commercial use and/or that the intellectual property rights/ownership rights have been transferred to you, or that you've received a license to use the i...
This is a tricky question as you are entering a gray area if you are using material from Book Z to inspire your own book. Derivatives works are highly litigated and there is case law that you could turn to to help you make this decision but based on your example its going to be a fine line. You w...