A long time ago, in a galaxy far, far away...
You go south to the equator from 60 degrees north (3600/60 = 60 degrees; on a meridian, so no complications).
you go east by another 60 degrees (3600/60 = 60 degrees; on a horizontal meridian, the equator, so no complications).
you go north by 60 degrees (3600/60 = 60 degrees; on a meridian, so no complications).
If you draw this (just rough, nothing exact) you will see that you are on the same latitude as the start point, but 60 degrees to the east of your original longitude, ie 30 east.
Head west 3600 nm at 60 degrees north? You are looking for the change of longitude, so apply departure: (3600/60)/(cos60) = 60/0.5 = 120 degrees west from 30 degrees east = 90 degrees west.
I hope.