It is known that the population growth model is given by:
[tex]P=P_0e^{kt}[/tex]Initial population is 225 so P0=225 so it follows:
[tex]P=225e^{kt}[/tex]Each year the population will increase by 25% so it follows:
[tex]\begin{gathered} P_0+0.25P_0=225e^k \\ e^k=\frac{5}{4} \\ k\ln e=\ln (\frac{5}{4}) \\ k\approx0.2231 \end{gathered}[/tex]So the population function is:
[tex]P=225e^{0.2231t}[/tex]The population in 5 years is given by:
[tex]P=225e^{0.2231\times5}\approx686.4960025[/tex]Hence the population of trout will be 686.4960025 after 5 years which can be rounded to 687.