Answer
$\begin{bmatrix}56&78&30\\60&57&26\end{bmatrix}$
Work Step by Step
In part a) we built the matrices $M$ and $J$:
$$M=\begin{bmatrix}31&42&18\\22&25&11\end{bmatrix}$$
$$J=\begin{bmatrix}25&36&12\\38&32&15\end{bmatrix}.$$
Determine $M+J$:
$$\begin{align*}
M+J&=\begin{bmatrix}31&42&18\\22&25&11\end{bmatrix}+\begin{bmatrix}25&36&12\\38&32&15\end{bmatrix}\\
&=\begin{bmatrix}31+25&42+36&18+12\\22+38&25+32&11+15\end{bmatrix}\\
&=\begin{bmatrix}56&78&30\\60&57&26\end{bmatrix}.
\end{align*}$$
The matrix $M+J$ represents the total sales in May and June for each store and each model.
