amy purchases 10 duplexes (a total of 20 rentable units) and she expects to have to replace the air conditioning equipment in each rentable unit 10 years from now at a cost of $1500 per unit. the bank that loaned amy the money to purchase the duplexes requires that she deposit a part of the monthly rents into an account earning 6 percent annual interest with monthly compounding to ensure that the money will be available to replace the air conditioning units. how much money per month must amy deposit?