Let $$A = \left[\begin{array}{ccc} -3 &1 &-3\cr 3 &5 &-3 \end{array}\right],$$ $$B = \left[\begin{array}{ccc} 2 &-1 &1\cr -1 &2 &3 \end{array}\right],$$ $$C = \left[\begin{array}{ccc} 1 &-3 &-3\cr 4 &4 &4 \end{array}\right].$$ If possible, compute the following. If an answer does not exist, enter DNE.

$(A + B) + C =$  help (matrices)

$A + (B + C) =$  help (matrices)

Choose True False True or False: $(A + B) + C = A + (B + C)$ for any three matrices $A$, $B$ and $C$ of the same size.