Answer: 0.321 seconds
Explanation:
Let assume that air has a temperature of 20 °C. Sound speed at given temperature is [tex]343 \frac{m}{s}[/tex]. As sound spreads at constant speed, time can be easily found by using this formula:
[tex]\Delta t = \Delta t_{far} - \Delta t_{near}[/tex]
[tex]\Delta t = \frac{x_{far}-x_{near}}{v_{sound,air}}[/tex]
[tex]\Delta{t} = \frac{120 m - 10 m}{343 \frac{m}{s} }\\\\\Delta {t} = 0.321 sec[/tex]