I think you are trying to ask how many ounces were used in order for 3 ounces to be left and if that is the case then the answer is 49 oz were used.
Step-by-step explanation:
There are about 16 oz to a pint. multiplying 16*3.25 gives the number of ounces: 52. Subtract 3 from 52 to get the number of oz used throughout the class