Arrange the layers in order from youngest to oldest.

example ; layer 2, layer 4

7,8,6,5,4,3,2,1

Working backwards (to get the oldest), we have layer 1 forming first, then 2 above it, then 3. 4, 5, and 6 formed and then a fault caused the right side to slide down. 8 is intrusive, you can tell it's newer than 1, 2, 3, 4, 5, and 6 because it reaches all of those layers. You can tell 7 is the youngest layer because it formed after the fault (it's not split like 4, 5, and 6) and after 8's intrusion (because 8 doesn't reach it).

"doesn't reach it" means it isn't in that layer.