28,900. According to old boys, we know that the 30% down payment is 2.4 million yuan, which is 66% interest. The monthly payment needs 28,900 yuan, and the total interest is 48 1 0,000 yuan. Monthly mortgage refers to the monthly repayment amount that the lender should pay to the lending bank during the repayment period, including the principal and corresponding interest, when purchasing commercial houses and motor vehicles by bank mortgage.