Step 2: determining the distance to the epicenter
you now know the difference between the arrival of the first p wave and the first s wave for each seismic station. because the waves travel at a known speed, this interval can be converted to distance using the graph below.

the p wave arrived at 8: 08: 00, and the s wave arrived at 8: 10: 30.
the difference is 2 minutes and 30 seconds, or 2 1/2

s-p wave interval chart

find 2 minutes and 30 seconds on the chart, then drop down to the distance when you intersect the s-p wave interval line = 1,600 km.

reading the graph: tips and practice
the major lines you read on the y-axis (vertical axis) are minutes. the minor lines are quarters of minutes. starting from 0, the first dotted line would be 15 seconds, then 30 seconds for second line, 45 seconds for the third line, and then 1 minute for the next solid line.
the major lines you read on the x-axis (horizontal axis) are in kilometers. each major line is 500 km. each dotted line is 250 km.
here are a few to practice.
1 minute = km
45 seconds = km
2 minutes and 45 seconds = km

check your answers:

example: