Math question

  1. You are about to set up a new retirement savings account that earns interest at a 3% annual interest rate (APR). You want to make monthly contributions to that account from now until you retire in 20 yrs. The goal is to save enough money so that you will be able to withdraw the money you need each month without depleting your principal (in reality, you will probably deplete your principal gradually). How much money do you need to contribute to the account each month?  

Please write out steps taken to get to the solution. Need this as soon as possible. Thanks