In my opinion, the best answer is in Rich dad poor dad, and it goes like this.
First, figure out your expenses.
Then earn money, and your income has to be greater than your expenses. Save and invest as much as you can.
Your investments should provide you some income, rent from your real estate acquisitions, stock dividends, bond yields etc. Once this income is greater than your expenses, you become wealthy.
After that point, NEVER spend more than your "passive" earnings, and keep increasing your investments with the extra money.
Great explanation. Yes that will work very well. If we can do that we should also be able to give a definite number as to how much will be sufficient for us.