From the given information, we know that the expression that models the population of amoebas with respect to time is:
[tex]P=8x^3[/tex]Where x is the number of hours. by replacing 9 for x, we can find the population after 9 hours, like this:
[tex]\begin{gathered} P=8\times9^3 \\ P=8\times729 \\ P=5832 \end{gathered}[/tex]Then, the population of amoebas after 9 hours is 5832.