The notation is saying you can get a 4% discount on you order if you pay within 10days. Or you can get a 2% discount if you pay within 20 days. If you don't pay with either, then the full amount is due in 30 days.
Since the invoice is dated July 27th and you pay it on August 10th, then 14 days have gone by. You are not within the 10 day window, but you are within the 20 day window and will receive a 2% discount. So now find 2% of 4465.97 and then subtract that result from 4465.97.