\[\left( y \cdot y^{2} \right)^{3}\ :\left( y \cdot y^{3} \right)^{2} =\]
\[= \left( y^{3} \cdot y^{6} \right)\ :\left( y^{2} \cdot y^{6} \right) =\]
\[= y^{3 + 6}\ :y^{2 + 6} =\]
\[\mathbf{=}y^{9}\mathbf{\ }:y^{8} = y^{9 - 8} = y.\]