Seismograph a records p waves at 6: 05 pm and s waves at 6: 10 pm. seismograph b records p waves at 6: 10 pm and s waves at 6: 25 pm. what is the difference in the arrival times at each device? which device is closer to the earthquake's epicenter?

For seismograph A, the lag time is
5 minutes (difference between 6:10 and 6:05)
For seismograph B, the lag time is
15 minutes (difference between 6:25 and 6:10)

Assuming that earthquake waves have a constant velocity during the earthquake, then the seismograph with the shorter lag time is closer to the epicenter. So,
Seismograph is closes to the earthquake's epicenter

What exactly do you mean 

Answer decreased soil salinity;