\(\therefore t \propto \frac{l}{A}\)
\(\Rightarrow \frac{{{t_1}}}{{{t_2}}} = \frac{{{l_1}}}{{{l_2}}} \times \frac{{{A_2}}}{{{A_1}}} = \left( {\frac{{{l_1}}}{{{l_1}/2}}} \right)\, \times \left( {\frac{{2{A_1}}}{{{A_1}}}} \right)\)
\(\Rightarrow \frac{{{t_1}}}{{{t_2}}} = 4\) \(⇒\) \({t_2} = \frac{{{t_1}}}{4} = \frac{{12}}{4} = 3\)