The seismogram below shows the record of ground shaking associated with an earthquake observed at a certain location. The first sign of the earthquake is the arrival of the P-wave. 45 seconds later, the S-wave arrives. Surface wave S-wave P-wave 45 seconds Time Let D be the distance between this location and the focus (origin) of the earthquake, and Vp and Vs be the speeds of P-wave and S-wave, respectively. (a) Express the time it takes for the P-wave and S-wave to travel between the focus and this location in terms of D, Vp and Vs. (b) Assuming Vp = 8 km/s (kilometer per second) and Vs = 4 km/s, compute D in km. Show your work