Physics??? speed of sound...

Question

the speed of sound through the ground is about 6.0km/s while the speed of sound is air is 343 m/s. A very powerful occurs some distance away and you feel the ground vibrate 60 seconds before you hear the sound of the explosion. how far away is the explosion?

Answer 1

(6000 m/s - 343 m/s) * 60 s

Answer 2

let t be the time it takes to travel through ground

distance through ground: 6t

distance through air: 0.343(60+t)

6t=0.343(60+t)

6t=20.58+0.343t

t=3.637970656 sec

distance = 6(3.637970656)= 21.82782393 km away

hope this helps