You have to look at the arrival time between the P and S waves. it looks like they already did it for you here. the answer is 1035 km.
I drew a couple extra lines to show you in more detail.
Let's say for example our p-wave arrived at t=4min and our s wave arrived at t=6.5 min. The time difference is 2.5 min. So you can either plot 4 and 6.5 and draw a line straight across like I did (green line and dotted green) or find the spot where the distance between the two lines is t = 2.5 min. We see the epicentral distance for the green line is about 1800km.
Try the yellow line yourself. you should get t values of about 4.5 and 8.5 at an epicentral distance of 2600km.
I drew a couple extra lines to show you in more detail.
Let's say for example our p-wave arrived at t=4min and our s wave arrived at t=6.5 min. The time difference is 2.5 min. So you can either plot 4 and 6.5 and draw a line straight across like I did (green line and dotted green) or find the spot where the distance between the two lines is t = 2.5 min. We see the epicentral distance for the green line is about 1800km.
Try the yellow line yourself. you should get t values of about 4.5 and 8.5 at an epicentral distance of 2600km.