Discussion ?'s Need today

Need to be 200 words long and have a reference. Format needs to be... question, answer, reference. question, answer, reference.

Can direct materials ever be irrelevant in a make-or-buy decision? Please explain. Give an example of a fixed cost that is relevant.

Please explain why depreciation on an existing asset is always irrelevant.

What is the basic flaw in the payback model?

Please explain the Internal Rate of Return and provide an example.