Given:
Loan=400000-downpayment=400000(1-0.2)=320,000
i=interest rate = 8% nominal = 0.08/12 per month
term=30 years => n=30*12=360
Question: what the the balloon payment at the end of the eighth year to pay off the mortgage.
Solution:
Monthly payment


=2348.0466 per month
At the end of the eighth year,
Future value of the loan
F1=320000(1+0.08/12)^(8*12)
=605586.310
Future value of payments


=314329.676
Therefore the balloon payment to pay off mortgage
=F1-F2
=605586.310-314329.676
=291256.63 (to the nearest cent)