Explain in a letter to your boss why it is okay to say \’no\’ at work.

Using the following blog:
http://a-new-way-to-work.com/2015/04/27/have-we-lost-the-ability-to-say-no-at-work/

*** Explain in a letter to your boss why it is okay to say \’no\’ at work. Write a business letter to your boss explaining why you are not able to complete a project that the manager requested you complete. ***