The scenario describes a population of rabbits that starts with 6 in year 0 and quadruples each year.
To express this mathematically:
- The starting population at year 0 is 6 rabbits.
- Each subsequent year, the number of rabbits is multiplied by 4.
Therefore, after \( x \) years, the number of rabbits can be represented by the function:
\[ f(x) = 6 \cdot (4)^x \]
So the correct choice is:
A. f(x) = 6(4)^x