Given, the initial population, Po=55000.
The rate of increase in population, R=3.1%.
Then, the population after x years can be given as,
[tex]\begin{gathered} f(x)=P_0(1+\frac{R}{100})^x \\ f(x)=55000(1+\frac{3.1}{100})^x_{} \\ =55000(1+0.031)^x \\ f(x)=55000(1.031)^x \end{gathered}[/tex]Therefore, the equation which models the population is,
[tex]f(x)=55000(1.031)^x[/tex]