Answer
a. The size of the matrix is $2\times 2$.
b. The element is $-1$.
Work Step by Step
a.
The size of the matrix is equal to number of rows multiply by number of columns.
The given matrix is
$\begin{bmatrix}
3& -1\\
4 & 7
\end{bmatrix}$
Number of rows $=2$.
and number of columns $=2$.
Hence, the size of the matrix is $2\times 2$.
b.
$(1,2)$ is a position at row $1$, column $2$.
The element at row $1$, column $2$ is $-2$.
Hence, the element is $-1$.
