The continuous random variable \(X\) has probability density function f given by
\[f(x)=\left\{\begin{array}{ll}
\frac{1}{80}\left(3 \sqrt{ } x-\frac{8}{\sqrt{ } x}\right) & 4 \leqslant x \leqslant 16 \\
0 & \text { otherwise. }
\end{array}\right.\]
(i) Find the distribution function of \(X\).

The random variable \(Y\) is defined by \(Y=\sqrt{ } X\).
(ii) Find the probability density function of \(Y\).