a
(a) Total time taken for both the echoes $t = {t_1} + {t_2} = 2\,sec$
but $t = \frac{{2{d_1}}}{v} + \frac{{2{d_2}}}{v}$
$ \Rightarrow t = \frac{2}{v}\left( {{d_1} + {d_2}} \right)$
$ \Rightarrow ({d_1} + {d_2}) = \frac{{v \times t}}{2} = \frac{{340 \times 2}}{2} =340m.$
