Final answer:
After four days, 1 big fish and 2 small fish died in the abandoned aquarium. There are 3 fish remaining in the aquarium.
Step-by-step explanation:
In the abandoned aquarium, there were initially 3 big fish and 3 small fish, making a total of 6 fish. After four days, 1 big fish and 2 small fish died. To find out how many fish remain, we subtract the number of fish that died from the initial total: 6 - 1 (big fish) - 2 (small fish) = 3 fish remaining in the aquarium.