Answer:
30 year mortgage
down payment = $330,000 x 20% = $66,000
debt = $330,000 - $66,000 = $264,000
monthly payment = $264,000 / 136.2834 (PV annuity factor, 360 periods, 0.667%) = $1,937.14
total payments = $1,937.14 x 360 = $697,370.40
total interest paid = $697,370.40 - $264,000 = $433,370.40
20 year mortgage
down payment = $330,000 x 20% = $66,000
debt = $330,000 - $66,000 = $264,000
monthly payment = $264,000 / 128.9825 (PV annuity factor, 240 periods, 0.583%) = $2,046.79
total payments = $2,046.79 x 240 = $491,229.60
total interest paid = $491,229.60 - $264,000 = $227,229.60
the 20 year mortgage charges $433,370.40 - $227,229.60 = $206,140.80 less interest