From the table
Rate of change in the number of fish in the lake between t=6 years and t=12 years
for t = 6 population of fish = 3600
for t = 12 population of fish = 14400
[tex]\begin{gathered} \text{Rate of chnage in the number of fish betw}een\text{ t = 6 and t = 12} \\ =\text{ }\frac{14400\text{ - 3600}}{12\text{ - 6}} \\ =\text{ }\frac{10800}{6} \\ =\text{ 1,800 fish per year} \end{gathered}[/tex]