\begin{enumerate} \item (i) Express \(\frac { 21 } { \sqrt { 7 } }\) in the form \(k \sqrt { 7 }\).
(ii) Express \(8 ^ { - \frac { 1 } { 3 } }\) as an exact fraction in its simplest form. \item Find \(\frac { d y } { d x }\) when