Refer to the data in exercise $2 .$ The estimated regression equation for those data is
$$\hat{y}=-18.4+2.01 x_{1}+4.74 x_{2}$$
$\begin{array}{l}{\text { a. Develop a point estimate of the mean value of } y \text { when } x_{1}=45 \text { and } x_{2}=15 \text { . }} \\ {\text { b. Develop a } 95 \% \text { prediction interval for } y \text { when } x_{1}=45 \text { and } x_{2}=15 \text { . }}\end{array}$