Although the speeds are different, but the two waves will
reach the same station so the same distance.
dp = ds
The formula for distance given velocity and time is:
d = v t
Substituting this to the 1st equation:
vp tp = vs ts
Since p wave arrived 2 min (120 s) earlier than s wave,
therefore
tp = ts - 120
Then,
vp (ts – 120) = vs ts
8.5 (ts – 120) = 5.5 ts
8.5 ts - 1020 = 5.5 ts
3 ts = 1020
ts = 340 s
tp = ts – 120 = 340 – 120 = 220 s
Then using either dp or ds, we can calculate how far away the
earthquake is:
dp = vp tp
dp = 8.5 * 220
dp = 1870 km = 1.9 * 10^3 km