Simple Bank over 23. Calculating Annuities You are planning to save for retirement over the net 30 years. To do this, you will invest $750 per month in a stock account and $250 pr month in a bond account. The return of the stock account is expected to be 11 percent per year, and the bond account will earn 6 percent per year. When you retire, you will combine your money into an account with an annual return of 8 percent. How much can you withdraw each month from your account assuming a 25-year withdrawal period