If y varies inversely as the square of x you can say that:
[tex]x^2y=k[/tex]Where k represents a constant.
For x=4 and y=8, then
[tex]\begin{gathered} (4)^28=k \\ k=128 \end{gathered}[/tex]Then for x=3
[tex]\begin{gathered} x^2y=k \\ y=\frac{k}{x^2} \\ y=\frac{128}{(3)^2} \\ y=\frac{128}{9} \\ y=14.2 \end{gathered}[/tex]