\[\boxed{\text{475\ (475).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[\textbf{а)}\ 81x^{4} = \left( 9x^{2} \right)^{2}\]
\[\textbf{б)}\ 121a^{6} = \left( 11a^{3} \right)^{2}\]
\[\textbf{в)}\ 0,09y^{12} = \left( 0,3y^{6} \right)^{2}\]
\[\textbf{г)}\frac{4}{9}b^{6} = \left( \frac{2}{3}b^{3} \right)^{2}\ \]