Answer:
Time taken, t = 0.5 seconds
Step-by-step explanation:
It is given that,
Speed of sound wave, v = 320 m/s
The sound reflects off of a boulder that is 80 m away.
Let t is the time taken to hear the echo. The distance covered by the sound to hear the echo is, 2d. So,

t = 0.5 seconds
So, the time taken to hear the echo is 0.5 seconds. Hence, this is the required solution.