I just need it solved in detailed steps

2.11 Assume that you work from age 25 to age 65. At the end of each year, you contribute C to your pension fund, which is invested at a yearly rate r = 5%. At age 65 you retire and plan to consume $20,000 each year, until you die. Assuming that you die at age 85, and that interest rates remain constant, how much should you save each year? How does the result change if, due to your reckless lifestyle, you assume that departure will occur at age 75? (Hint: Use Problem 2.10.)