Hint for process of elimination: First, pay close attention to which set is contained in which set and their pairwise relative size. This can help you get a good estimate of what the answer to this question is, or possibly lead you to the exact answer. Second, draw a picture of this system. That might give you a visual representation of how large set A is compared to set C. Third, the answer choices range from a low of 4% to a high of 96%. This massive range in percent values is about as big as a range can or will get on an SAT. Enormous differences in sizes of the answer choices should allow you to eliminate some of them. Fourth, The answer should be lower than 20%, so use that to eliminate choices.
Read on for a full solution.
Solution: Set A is 20% of set B, and set B is 20% of set C. Therefore, set A is 20% of 20% of set C, or $latex 0.20 \times 0.20 = 0.04 = 4\% $ of set C.