Payment on $80K at 10% for 30 years is $702.06. You can calculate that with a financial calculator or in Excel. In Excel, the formula is: -PMT(10%/12,30*12,80000)
After five years, the balance on the loan will be $77,259.46. You calculate that with the FV function:
Not quite sure what your intention is after the $30K payment. Typically a balloon payment would mean the entire loan must be paid at that time. So a "five year balloon" would mean the loan is to be paid off after five years.
So, maybe you mean the payments continue at the same $702.06 payment after the $30K payment. If so, the question is how many payments remain. You would calculate that with the NPER (number of periods) function:
The answer is 99 payments plus a partial payment would still need to be make.
If instead you meant you want the loan to only have $30K remaining balance after five years, then you need to use a shorter amortization than 30 years. In that case you would calculate the payment using the PMT function and a future value of $30K after five years. That payment is $1,312.35, which equates to a 85.5 month amortization period.