What would be the amount of check issued for 08/11 invoice for $648.50 paid on 09/13 with the terms (3/10, 2/15, n30-5% apr)?

I'm assuming this is a homework problem so I won't just give you the answer, but I'll explain the terms.

3/10 means you can take a 3% discount if you pay the invoice within 10 days.

2/15 means you take a 2% discount if you pay with 15 days.

n30 means you pay the net amount of the invoice (the $648.50) if you pay within 30 days.

5% apr means you owe interest at the rate of 5% per year if you pay after 30 days. You have to calculate that interest based on when you pay the invoice.