Explanation:
attention : this is either a trick question, or a very badly phrased question !
as it is phrased, the question is really only about the fraction of the lemonade, and not about the fraction of the volume of the pitcher.
so, the available lemonade (it does not matter how much it is, and how much it fills the pitcher) is equally split into 6 parts.
therefore, each cup gets 1/6 of the lemonade.
now, if the question was badly phrased and really asked about the fraction of the pitcher volume in every cup, then the calculation would be dividing the original 3/4 of the pitcher by 6 :
3/4 / 6 = 3/4 / 6/1 = (3×1) / (4×6) = 3/24 = 1/8
each of the 6 cups would get 1/8 of the pitcher's volume.