c
(c) Given, $kA = \left[ {\,\begin{array}{*{20}{c}}0&{3a}\\{2b}&{24}\end{array}\,} \right]$
==> $k\,\,\left[ {\begin{array}{*{20}{c}}0&2\\3&{ - 4}\end{array}} \right]\, = \,\left[ {\begin{array}{*{20}{c}}0&{3a}\\{2b}&{24}\end{array}} \right]$
==> $2k = 3a,\,3k = 2b,\, - 4k = 24$
==> $a = \frac{{2k}}{3},\,\,\,b = \frac{{3k}}{2},\,k = - 6$
$ \Rightarrow $ $k = - 6,\,\,a = - 4,\,b = - 9$.