Analyzing the function, we can see that the initial value of the function is 771 (f(0) = 771).
Also, this value will be multiplied by 4 when its exponent is equal to 1.
Since the exponent of 4 is equal to t/3, let's equate the exponent to 1:
![\begin{gathered} (t)/(3)=1 \\ t=3\cdot1 \\ t=3 \end{gathered}](https://img.qammunity.org/2023/formulas/mathematics/college/uuef4ovlhvyl8iay9ak280qs3pd00veiqu.png)
Therefore, when t = 3, the initial value of 771 will be multiplied by 4.
Also, for each increase of 3 years, the population will be multiplied by 4, since the exponent increases by 1.
So the answer is 3 years.