Answer:
Her mistake was in how many bags would be able to equally hold 4 bars.
325/4 is 81.25, which would mean there needs to be 82 bags, in which you wouldnt be able to hold 4 each equally.
A better option for Paz is to put 5 bars in each bag as 325 is an even multiple of 5. As such would result in the bag count being brought down to 65 bags to evenly hold all of the bars.
Hope this helped!