3 The continuous random variable \(X\) has cumulative distribution function F given by $$F ( x ) = \begin{cases} 0 & x < 0
\frac { 1 } { 81 } x ^ { 2 } & 0 \leqslant x \leqslant 9
1 & x > 9 \end{cases}$$

1. Find \(\mathrm { E } ( \sqrt { X } )\).
2. Find \(\operatorname { Var } ( \sqrt { X } )\).
3. The random variable \(Y\) is given by \(Y ^ { 3 } = X\). Find the probability density function of \(Y\).