6. Princess Kim is currently 20 years old. She wants to buy insurance to guarantee her retirement life after retirement. When retirement age reaches 60, we intend to spend 18 million won every year for 20 years therefrom. If so, how much should Princess Kim accumulate annually over the next 40 years? However, it is assumed that insurance premiums are accumulated and repaid at the end of each year, and the market interest rate by period is constant at 10%.