In order to determine the number of hours it will take for the sound to travel a certain distance, we divide the given distance by the speed. Mathematically,
time = distance / speed
Substituting the known values,
time = (7.2 x 10^2 km) / (1.2 x 10^3 km/h)
time = 0.6 h
The answer given above is already in the correct number of significant figures. Therefore, the answer is 0.6 hours.