Row 1, column 1:
Hint: Row 1 of $A$ is $\begin{pmatrix} 6 & 4 \end{pmatrix}$. Column 1 of $B$ is $\begin{pmatrix} -7 \\ 3 \end{pmatrix}$. Multiply in pairs and add the results.
Row 1, column 2:
Hint: Row 1 of $A$ is $\begin{pmatrix} 6 & 4 \end{pmatrix}$. Column 2 of $B$ is $\begin{pmatrix} 8 \\ -1 \end{pmatrix}$. Multiply in pairs and add the results.
Row 2, column 1:
Hint: Row 2 of $A$ is $\begin{pmatrix} 2 & 5 \end{pmatrix}$. Column 1 of $B$ is $\begin{pmatrix} -7 \\ 3 \end{pmatrix}$. Multiply in pairs and add the results.
Row 2, column 2:
Hint: Row 2 of $A$ is $\begin{pmatrix} 2 & 5 \end{pmatrix}$. Column 2 of $B$ is $\begin{pmatrix} 8 \\ -1 \end{pmatrix}$. Multiply in pairs and add the results.