If $$A = \left[\begin{array}{cccc} -3 &1 &-3 &3\cr 5 &-3 &2 &-1\cr 1 &-1 &2 &3 \end{array}\right],$$ determine the following entries:

$a_{3 4} =$
$a_{2 1} =$
$a_{1 3} =$