Find the value of $x$ for which the matrix product $\left[\begin{array}{ccc}2& 0& 7\\ 0& 1& 0\\ 1& -2& 1\end{array}\right]\left[\begin{array}{ccc}-x& 14x& 7x\\ 0& 1& 0\\ x& -4x& -2x\end{array}\right]$ equal to an identity matrix.

In the matrix, write :
$A=\left[\begin{array}{c}2\\ 35\\ \sqrt{3}\end{array}\begin{array}{c}5\\ -2\\ 1\end{array}\begin{array}{c}19\\ \frac{5}{2}\\ -5\end{array}\begin{array}{c}-7\\ 12\\ 17\end{array}\right]$

(i) The order of the matrix
(ii) The number of elements 
(iii) Write the elements $a_{13},a_{21},a_{33},a_{24},a_{23}$