$$\root 3 \of {\sqrt {0.000064} } = ?$$

$$\eqalign{ & = \sqrt {0.000064} \cr & = \sqrt {\frac{{64}}{{{{10}^6}}}} \cr & = \frac{8}{{{{10}^3}}} \cr & = \frac{8}{{1000}} \cr & = 0.008 \cr & \therefore \root 3 \of {\sqrt {0.000064} } \cr & = \root 3 \of {0.008} \cr & = \root 3 \of {\frac{8}{{1000}}} \cr & = \frac{2}{{10}} \cr & = 0.2 \cr} $$