\[\sqrt[3]{4a^{2}}\ :\sqrt[6]{8a^{2}} = \frac{\left( 2^{2} \right)^{\frac{1}{3}}a^{\frac{2}{3}}}{\left( 2^{3} \right)^{\frac{1}{6}}a^{\frac{2}{6}}} =\]
\[= \frac{2^{\frac{2}{3}}a^{\frac{2}{3}}}{2^{\frac{1}{2}}a^{\frac{1}{3}}} = 2^{\frac{4}{6} - \frac{3}{6}}a^{\frac{2}{3} - \frac{1}{3}} =\]
\[= 2^{\frac{1}{3}}a^{\frac{1}{3}} = \sqrt[3]{2a}.\]