Answer: 64 ounces each
Explanation:
1 gallon = 128 ounces
128 ounces x 2 gallons = 256 ounces
256/4 = 64 ounces
OR
Each friend got 1/2 gallon each. If there are 2 gallons then there would be 4 'halves'. 2 halves per gallon and there are 2 gallons.
(I am not sure what the answer choices are.)