Answer: The function would be,

Explanation:
Given,
Park rangers released 12 fish into a pond in year 0,
Thus, the initial number of fish = 12,
Also, there were twice as many fish as the year before,
⇒ After 1 year the number of fishes = 2(12) = 12(2),
Similarly,
After 2 years = 2(12(2))= 12(2)²,
After 3 years = 2(12(2)²) = 12(2)³,
................, so on,....
Thus, the number of fishes after x years would be,

Let f(x) represents the number of fish after x years,

Which is the required function that the given scenario.