\[\boxed{\text{283\ (283).}\text{\ }\text{Еуроки\ -\ ДЗ\ без\ мороки}}\]
\[5x^{2}y^{4} = 6;\ \ \ \ \ \ x^{2}y^{4} = \frac{6}{5} = 1,2\]
\[1)\ 1,5x^{2}y^{4} = 1,2 \cdot 1,5 = 1,8\]
\[2)\ 25x^{4}y^{8} = \left( 5x^{2}y^{4} \right)^{2} = 6^{2} =\]
\[= 36\]
\[3) - 25x^{6}y^{12} = - 5^{2} \cdot \left( x^{2}y^{4} \right)^{3} =\]
\[= - 25 \cdot \left( \frac{6}{5} \right)^{3} = - 25 \cdot \frac{216}{125} =\]
\[= - \frac{216}{5} = - \frac{432}{10} = - 43,2\]