Amoritization schedule with periodic payments and Balance due

Amoritization schedule with periodic payments and Balance due

I borrowed $25,000 for 24 months, agreed to pay back $35000 in a single balloon payment at the end of the 24th month.  However, what actually occurred is this:  I made a $1200 payment the first day the loan was given.  I made a $500 payment after 30 days.  I made another $500 payment on month 13, and on months 18 thru 24, I made (6) $500 payments.  My question is what is the balance actually due using simple interest and with the periodic payments made?