## Solution:

We know that 1 km=1000 m and 1 hr=3600 sec.

Convert 342 m/s.

$\displaystyle 342\:m/s=\left(342\:\frac{m}{s}\right)\left(\frac{1\:km}{1000\:m}\right)\left(\frac{3600\:s}{1\:hr}\right)=1231.2\:km/hr$          ☚

Therefore, the speed of sound in km/hr is 1231.2 km/hr.