A boy stands x\ m away from a high wall and claps his hands at a...

Time taken for $60$ claps is $2$ minutes $= 120\ \text{s}$.

Time interval between two consecutive claps is $T = \dfrac{120}{60} = 2\ \text{s}$.

Let the distance of the boy from the wall be $x$. The sound travels a distance of $2x$ (to the wall and back) to form an echo.

Time taken for the echo to return is $t = \dfrac{2x}{v}$.

Since each clap coincides with the echo of the previous one, the time for the echo to return equals the time interval between claps, so $t = T$.

$\dfrac{2x}{340} = 2$

$2x = 680$

$x = 340\ \text{m}$

Answer: $340\ \text{m}$