Finding the Dimensions of the Given Matrix and Locating Entries

Given matrix $A:$

ⓐWhat are the dimensions of matrix $A?$
ⓑWhat are the entries at $a_{31}$ and $a_{22}?$
$$A=\left[\begin{array}{cccc}2& & 1& 0\\ 2& & 4& 7\\ 3& & 1& -2\end{array}\right]$$

OpenStax, Algebra and Trigonometry 2e · §11.5 Matrices and Matrix Operations · Example 3