To find the answer you must first subtract the flat rate from 10.65
10.65- 4.25= 6.40
So now to find the price per ounce you must divide 6.40 by the amount of ounces (which in this case is 64 ounces since there are 16 ounces in a pound)
So 6.40 divided by 64 is 0.01
So Carl has to pay 1 cent per ounce