You are applying for a 30-year, fixed-rate (APR 6.50%), monthly-payment-required mortgage loan for a house that sells for $80,000 today. The mortgage bank will ask you for 20% initial down payment (in cash, paid immediately) of the house value, and charge you an extra $3,000 closing cost (carried into loan balance and amortized later) when the loan is approved. What should be your monthly loan payment (assuming payment is due by the end of each month)? 

10 years after buying the house, what will be the remaining principal balance of your loan?  (Hint:  For a loan or investment, the beginning loan balance is the same as "present value", whereas the ending or remaining balance is the same as "future value".  And please don't forget this is a monthly loan.)

10 years after buying the house (as Part b aforementioned), the loan market rate drops from 6.50% APR to 4.50% APR, you want to refinance on the remaining loan principal balance, but the bank will charge you an extra $4,000 refinancing fee (carried into the remaining loan balance and amortized later).  Would you be able, and by how much, to lower your monthly loan payment if you choose to refinance over the remaining loan life (i.e., instead of the extension of another 30 years)?  Based on your calculation results, should you choose to refinance or not?