Find the inverse of the matrix (if it exists)

$A=\left[\begin{array}{ccc}1& 2& 3\\ 0& 2& 4\\ 0& 0& 5\end{array}\right]$

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 $a_{13},a_{21},a_{33},a_{24},a_{23}$