\(\sqrt{4^{6x^{2}}}=4^{3x^{2}}\), \(\sqrt{25^{\,y/2}}=25^{y/4}=(5^{2})^{y/4}=5^{y/2}\),
\(\sqrt{9}=3\), \(\sqrt{z^{4}}=z^{2}\) (assuming \(z\ge 0\)).
Multiply: \(4^{3x^{2}}..... 5^{y/2}..... 3..... z^{2}\).
\[
\boxed{4^{3x^{2}}..... 5^{y/2}..... 3\,z^{2}}
\]