Given the Following Matrix $B = \left[ \begin{array} { c } \frac { 2 } { 3 } \\4 \\0 \\- \frac { 6 } { 7 }\end{array} \right]$

Short Answer

Given the following matrix.
$B = \left[ \begin{array} { c } \frac { 2 } { 3 } \\4 \\0 \\- \frac { 6 } { 7 }\end{array} \right]$
What are the dimensions
$\_\_\_\_\_\_\_\text { x }\_\_\_\_\_\_\_$
What is the value of the element $b _ { 31 }$
$b _ { 31 } =\_\_\_\_\_\_\_$