Sally takes out a mortgage with the following repayment schedule: -$100 at the beginning of each month in year 1 -$200 at the beginning of each month in year 2 -... -$100 x n at the beginning of each month in year n -... -$1,500 at the beginning of each month in year 15. Sally will pay interest at an effective annual rate of 7%. Determine the present value of Sally's loan payments at the beginning of year 1, just before she makes her first $100 payments.