The velocity of the transverse waves produced by an earthquake is 7.2 km/s, while that of the longitudinal waves is 4.2 km/s. A seismograph records the arrival of the transverse waves 68 s before that of the longitudinal waves. How far away was the earthquake?

Answer 1

Same distance D for both
distance = speed * time
D = 7.2 t
D = 4.2(t+68)
so
7.2 t = 4.2(t+68) solve for t
then use that t in D=7.2 t
to get D, the distance

Answer 2

D = 685.44 km

Thanks a lot!!