You are planning to save for retirement for the next 15 years. You will invest $1,000 a month in a stock account and $600 a month in a bond account. The return of the stock account is expected to be 12%, and the bond account will pay 7%. When you retire, you will combine your money into an account providing 9% return. Assuming a 20-year withdrawal period, how much can you withdraw each month from your account?