assuming average income of $70000 per year, what is the lump-sum you need at retirement assuming that you will need approximately 80% of your...

assuming average income of $70000 per year, what is the lump-sum you need at retirement assuming that you will need approximately 80% of your disposable income upon retirement. you will retire in 40 years and you plan on living another 25 years after retirement. you feel you can earn 12%, and you expect a 5% inflation rate over the 40 years.