Greg Mendoza has just slept through the class in which Professor Conway explained the concept of depreciation. Because the next test is scheduled for Wednesday, Mendoza telephones Leah Gerbing to get her notes from the lecture. Gerbing's notes are concise: "DepreciationSounds like Greek to me." Mendoza next tries Ray Mellichamp, who says he thinks depreciation is what happens when an asset wears out. Sally Bower is confident that depreciation is the process of building up a cash fund to replace an asset at the end of its useful life. Explain the concept of depreciation for Mendoza. Evaluate the explanations of Mellichamp and Bower. Be specific.