$K\,\, = \,\,\frac{{2.303}}{t}\log \frac{{100}}{{0.1}}$ ............ $(2)$
$(1) = (2)$
$\frac{{2.303}}{{32}}\,\log \,100 = \frac{{2.303}}{t}\log \frac{{100}}{{0.1}}$
$\frac{2}{{32}} = \frac{3}{t}$
$\Rightarrow t = 48\,\min.$