Question: The function \(f\left( x \right)\) is a probability distribution

\[f\left( x \right)=\left\{ \begin{aligned} & \frac{2}{9}\left( 3-x \right)\,\,\,\,\,\,\,\,\,0\le x\le 3 \\ & 0\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\,\text{otherwise} \\ \end{aligned} \right.\]

Compute \(\Pr \left( 1\le X\le 2 \right)\).