What amount must be deposited in an account that earns 10% on January 1, 2017 if an investor wants to withdraw $5,000 January 1 of each year beginning on January 1, 2018 with the last withdrawal being made on January 1, 2021? What if the withdrawals take place on December 31 of each year starting on December 31, 2017 until December 31, 2020? What if withdrawals of $2,500 occur every six months on June 30 and Dec 31 of each year starting on June 30, 2017 until December 31, 2020?