If $I_3$ denotes identity matrix of order $3\times 3$, write the value of its determinant.

Let $A=\left[a_{ij}\right]$ be a square matrix of order $3\times 3$ and $C_{ij}$ denote cofactor of $a_{ij}$ in $A$. If $\left|A\right|=5$, write the value of $a_{31}{C}_{31}+a_{32}{C}_{32}+a_{33}{C}_{33}$

Let $A=\left[a_{ij}\right]$ be a square matrix of order $3\times 3$ and $C_{ij}$ denote cofactor of $a_{ij}$ in $A$. If $\left|A\right|=5$, write the value of 

 $a_{11}{\mathrm{C}}_{21}+a_{12}{\mathrm{C}}_{22}+a_{13}{\mathrm{C}}_{23}$.