Michael is an Internet service provider. On December 31, 2014, he bought an existing business with servers and a building worth $400,000. During 2015, his business grew and he bought new servers for $500,000. The market value of some of his older servers fell by $100,000. What was Michael's gross investment, depreciation, and net investment during 2015? What is the value of Michael's capital at the end of 2015?