Answer
$\left[\begin{array}{c c} 1& -7/2& 1/6\\ 0& 1/2&-1/6\\ 0& 0&1/3\end{array} \right]$
Work Step by Step
Using a graphing calculator (see attached picture), we get the inverse matrix:
$\left[\begin{array}{c c} 1& -7/2& 1/6\\ 0& 1/2&-1/6\\ 0& 0&1/3\end{array} \right]$
