You are just turned 30 years old. You have two children. One will go to university overseas 10 years from now and requires four beginning-of-year payments for university expenses of $10,000, $11,000, $12,000 and $13,000. The second child will go to another overseas university in 15 years from now and require four beginning-of-year payments for university expenses of $15,000, $16,000, $17,000 and $18,000. In addition, you plan to retire in 30 years and want be able to withdraw $50,000 per year (at the end of each year) from an account throughout your retirement. You expect to live 40 years beyond retirement. The first withdrawal will occur on your 51^stbirthday. Can you please explain step by step the calculation processes.