Compute the following:
$\left[\begin{array}{ccc} -6 &1 &-6\cr 5 &9 &1\cr -5 &4 &-2 \end{array}\right] + \left[\begin{array}{ccc} 2 &-2 &4\cr 5 &1 &-6\cr 1 &-5 &6 \end{array}\right] =$ $\left[\Rule{0pt}{3.6em}{0pt}\right.$$\left]\Rule{0pt}{3.6em}{0pt}\right.$