A 20-year-old man wants to plan for retirement. His annual income is $100,000 in real terms and remains constant. He has 40 years to work and plans to retire at the end of age 60. He wants to save for 30 years expected life after retirement. He desires to have an annual retirement income equal to 70% of pre-retirement income. Real interest rate is 5%. a) Determine how much of his current annual income he should save and how much to spend for current consumption. b) Assume he wants to give $30,000 to his grandchildren when he turns 80 and leave for charity $40,000 at the end of his life. Calculate how much he should save per year in this case.