West
You see whether your location is located to the east or west of the Prime Meridian. If it is located east of the Prime Meridian, then it is east longitude, and the same goes for west.
Concord is located to the west of the prime meridian.
China is located on the east side of the prime meridian.
Pittsburgh PA is located WEST of the Prime Meridian.
Both, but mostly east.
90° west longitude
The longitude of Cairo is 31°22′E, therefore it is located east of the Prime Meridian.
A small proportion is, most of Africa is east of the prime meridian.
Trick question. All lines of longitude meet at the poles.
Longitude
The majority of Europe is located east of the Prime Meridian.