Please explain quickly its urgent

Please explain quickly its urgent Sunil is standing between two parallel walls. The wall closest to him is at a distance of 660 m. If he shouts, he hears the first echo after 4 s and another after another 2 seconds. What is the velocity of sound in air? €2. What is the distance between the two walls? (Ans: 330 m/s; 1650 m

Dear student,
The sound first travels from Sunil to first wall and then travels back to him.
So total distance travelled by sound= 2*660=1320m
Time taken by Sound= 4 Seconds
So speed Of sound=
Distance traveled/Timetaken
=1320/4=330m/s
Distance traveled by second echo= 6 x 330 =1980 m Distance of 2nd wall from Sunil=1980 /2=990m
Distance between two walls= 990+660=1650m
Regards